Missing test files in 1.8.0 tarball

[Michał Górny]

It seems that 1.8.0 release is missing data files required by the newly added tests:

```
$ tox -e py39
py39 create: /tmp/pkginfo-1.8.0/.tox/py39
py39 develop-inst: /tmp/pkginfo-1.8.0
py39 installed: # Editable install with no version control (pkginfo==1.8.0),-e /tmp/pkginfo-1.8.0
py39 run-test-pre: PYTHONHASHSEED='2931678448'
py39 run-test: commands[0] | python setup.py test -q
running test
WARNING: Testing via this command is deprecated and will be removed in a future version. Users looking for a generic test entry point independent of test runner are encouraged to use tox.
running egg_info
writing pkginfo.egg-info/PKG-INFO
writing dependency_links to pkginfo.egg-info/dependency_links.txt
writing entry points to pkginfo.egg-info/entry_points.txt
writing requirements to pkginfo.egg-info/requires.txt
writing top-level names to pkginfo.egg-info/top_level.txt
reading manifest file 'pkginfo.egg-info/SOURCES.txt'
adding license file 'LICENSE.txt'
writing manifest file 'pkginfo.egg-info/SOURCES.txt'
running build_ext
......E........................E.........E.........E.....................................................................................................................
======================================================================
ERROR: test_ctor_w_valid_wheel_w_description_header (pkginfo.tests.test_wheel.WheelTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/pkginfo-1.8.0/pkginfo/tests/test_wheel.py", line 80, in test_ctor_w_valid_wheel_w_description_header
    wheel = self._makeOne(filename, metadata_version='1.1')
  File "/tmp/pkginfo-1.8.0/pkginfo/tests/test_wheel.py", line 11, in _makeOne
    return self._getTargetClass()(filename, metadata_version)
  File "/tmp/pkginfo-1.8.0/pkginfo/wheel.py", line 16, in __init__
    self.extractMetadata()
  File "/tmp/pkginfo-1.8.0/pkginfo/distribution.py", line 115, in extractMetadata
    data = self.read()
  File "/tmp/pkginfo-1.8.0/pkginfo/wheel.py", line 21, in read
    raise ValueError('No such file: %s' % fqn)
ValueError: No such file: /tmp/pkginfo-1.8.0/docs/examples/distlib-0.3.1-py2.py3-none-any.whl

======================================================================
ERROR: test_ctor_w_tar (pkginfo.tests.test_sdist.SDistTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/pkginfo-1.8.0/pkginfo/tests/test_sdist.py", line 45, in test_ctor_w_tar
    sdist = self._makeOne(filename)
  File "/tmp/pkginfo-1.8.0/pkginfo/tests/test_sdist.py", line 14, in _makeOne
    return self._getTargetClass()(filename)
  File "/tmp/pkginfo-1.8.0/pkginfo/sdist.py", line 13, in __init__
    self.extractMetadata()
  File "/tmp/pkginfo-1.8.0/pkginfo/distribution.py", line 115, in extractMetadata
    data = self.read()
  File "/tmp/pkginfo-1.8.0/pkginfo/sdist.py", line 40, in read
    archive, names, read_file = self._get_archive(fqn)
  File "/tmp/pkginfo-1.8.0/pkginfo/sdist.py", line 18, in _get_archive
    raise ValueError('No such file: %s' % fqn)
ValueError: No such file: /tmp/pkginfo-1.8.0/docs/examples/mypackage-0.1.tar

======================================================================
ERROR: test_ctor_w_tar (pkginfo.tests.test_sdist.UnpackedSDistGivenDirectoryTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/pkginfo-1.8.0/pkginfo/tests/test_sdist.py", line 45, in test_ctor_w_tar
    sdist = self._makeOne(filename)
  File "/tmp/pkginfo-1.8.0/pkginfo/tests/test_sdist.py", line 135, in _makeOne
    archive, _, _ = self._getTargetClass()._get_archive(filename)
  File "/tmp/pkginfo-1.8.0/pkginfo/sdist.py", line 18, in _get_archive
    raise ValueError('No such file: %s' % fqn)
ValueError: No such file: /tmp/pkginfo-1.8.0/pkginfo/tests/../../docs/examples/mypackage-0.1.tar

======================================================================
ERROR: test_ctor_w_tar (pkginfo.tests.test_sdist.UnpackedSDistGivenFileSDistTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/pkginfo-1.8.0/pkginfo/tests/test_sdist.py", line 45, in test_ctor_w_tar
    sdist = self._makeOne(filename)
  File "/tmp/pkginfo-1.8.0/pkginfo/tests/test_sdist.py", line 135, in _makeOne
    archive, _, _ = self._getTargetClass()._get_archive(filename)
  File "/tmp/pkginfo-1.8.0/pkginfo/sdist.py", line 18, in _get_archive
    raise ValueError('No such file: %s' % fqn)
ValueError: No such file: /tmp/pkginfo-1.8.0/pkginfo/tests/../../docs/examples/mypackage-0.1.tar

----------------------------------------------------------------------
Ran 169 tests in 0.170s

FAILED (errors=4)
Test failed: <unittest.runner.TextTestResult run=169 errors=4 failures=0>
error: Test failed: <unittest.runner.TextTestResult run=169 errors=4 failures=0>
ERROR: InvocationError for command /tmp/pkginfo-1.8.0/.tox/py39/bin/python setup.py test -q (exited with code 1)
_______________________________________________________________ summary _______________________________________________________________
ERROR: py39: commands failed
```

[Tres Seaver (tseaver)]

Thanks for the report!