non-fatal error in Postgresql installation

[TIm Harris]

During apt-get installation of Postgresql 9.5.2-1 on 16.04 LTS the following error occurs:

Building PostgreSQL dictionaries from installed myspell/hunspell packages...
Removing obsolete dictionary files:
Setting up postgresql-9.5 (9.5.2-1) ...
Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/(?<!\\)\${ <-- HERE ([^}]+)}/ at /usr/sbin/pam_getenv line 78.
Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/(?<!\\)\${ <-- HERE ([^}]+)}/ at /usr/sbin/pam_getenv line 78.
Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/(?<!\\)\${ <-- HERE ([^}]+)}/ at /usr/sbin/pam_getenv line 78.
Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/(?<!\\)\${ <-- HERE ([^}]+)}/ at /usr/sbin/pam_getenv line 78.
Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/(?<!\\)\${ <-- HERE ([^}]+)}/ at /usr/sbin/pam_getenv line 78.
Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/(?<!\\)\${ <-- HERE ([^}]+)}/ at /usr/sbin/pam_getenv line 78.
Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/(?<!\\)\${ <-- HERE ([^}]+)}/ at /usr/sbin/pam_getenv line 78.
Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/(?<!\\)\${ <-- HERE ([^}]+)}/ at /usr/sbin/pam_getenv line 78.
Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/(?<!\\)\${ <-- HERE ([^}]+)}/ at /usr/sbin/pam_getenv line 78.
Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/(?<!\\)\${ <-- HERE ([^}]+)}/ at /usr/sbin/pam_getenv line 78.
Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/(?<!\\)\${ <-- HERE ([^}]+)}/ at /usr/sbin/pam_getenv line 78.
Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/(?<!\\)\${ <-- HERE ([^}]+)}/ at /usr/sbin/pam_getenv line 78.
Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/(?<!\\)\${ <-- HERE ([^}]+)}/ at /usr/sbin/pam_getenv line 78.
Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/(?<!\\)\${ <-- HERE ([^}]+)}/ at /usr/sbin/pam_getenv line 78.
Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/(?<!\\)\${ <-- HERE ([^}]+)}/ at /usr/sbin/pam_getenv line 78.
Creating new cluster 9.5/main ...
  config /etc/postgresql/9.5/main

the error is not fatal and postgresql continues to install.

postgresql:
  Installed: 9.5+173
  Candidate: 9.5+173
  Version table:
 *** 9.5+173 500
        500 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
        500 http://us.archive.ubuntu.com/ubuntu xenial/main i386 Packages
        100 /var/lib/dpkg/status