gem has no manpage, warning about dangling symlink

[Aminda Suomalainen]

When I run `man gem` (or actually `LC_ALL=C man gem` in order to get the error in English) I receive:

```
man: warning: /usr/share/man/man1/gem.1.gz is a dangling symlink
No manual entry for gem
See 'man 7 undocumented' for help when manual pages are not available.
```

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: ruby 1:2.1.0.4ubuntu1
ProcVersionSignature: Ubuntu 3.19.0-22.22-generic 3.19.8-ckt1
Uname: Linux 3.19.0-22-generic x86_64
NonfreeKernelModules: fglrx
ApportVersion: 2.17.2-0ubuntu1.1
Architecture: amd64
CurrentDesktop:

Date: Wed Jul 22 11:54:17 2015
InstallationDate: Installed on 2015-07-14 (7 days ago)
InstallationMedia: Ubuntu-MATE 15.04 "Vivid Vervet" - Release amd64 (20150422.1)
PackageArchitecture: all
SourcePackage: ruby-defaults
UpgradeStatus: No upgrade log present (probably fresh install)