Remove distro-info package to try to get travisci working again

All environments on travis-ci are throwing:

pkg_resources.extern.packaging.version.InvalidVersion: Invalid
  version: '0.23ubuntu1' (package: distro-info)

when builiding gpgme.

Net suggestions include removing the offending distro-info.
Let's see if it works.

Author: rouilj

.travis.yml

@@ -53,6 +53,10 @@ addons:
       - gpgsm
 
 before_install:
+  # deal with setuptools error:
+  # pkg_resources.extern.packaging.version.InvalidVersion: Invalid
+  #    version: '0.23ubuntu1' (package: distro-info)
+  - sudo apt-get remove distro-info
   # build xapian
   - echo "$TRAVIS_PYTHON_VERSION"
   # Sphinx required to build the xapian python bindings. Use 1.8.5 on