Set language to "en" for documentation

Signed-off-by: Alec Delaney <tekktrik@gmail.com>

docs/conf.py

@@ -59,7 +59,7 @@
 #
 # This is also used if you do content translation via gettext catalogs.
 # Usually you set "language" from the command line for these cases.
-language = None
+language = "en"
 
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.