docs: define version number only once in config file

docs/conf.py

@@ -52,11 +52,7 @@ copyright = '2015-2018, Project Gluon'
 # The version info for the project you're documenting, acts as replacement for
 # |version| and |release|, also used in various other places throughout the
 # built documents.
-#
-# The short X.Y version.
-version = '2018.1+'
-# The full version, including alpha/beta/rc tags.
-release = '2018.1+'
+version = release = '2018.1+'
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.