Fix docs for environment markers in extras
Fix docs for environment markers in extras

The docs for environment markers in setup.cfg [extras] had a
couple of issues.

1) There was a space after the package name.
2) python_environment was used where python_version is the marker.

Change-Id: Idbc72c45ae240356ca39eeba6db754f56c6a0f23

varunarya10/pbr,openstack-dev/pbr,JioCloud/pbr,WiFast/pbr,klmitch/pbr,WiFast/pbr,varunarya10/pbr,openstack-dev/pbr,openstack-dev/pbr,JioCloud/pbr,klmitch/pbr