[gnome-builder] doc: specify specific rtd theme

[Christian Hergert <chergert src gnome org>]

commit 3a978fe25580af9a633c80efcdfd7b229ec88af4
Author: Christian Hergert <chergert redhat com>
Date:   Wed Feb 22 12:53:23 2017 -0800

    doc: specify specific rtd theme
    
    We can use 'default', but this allows things to look proper when building
    locally so we don't have to upload to test.
    
    To install the rtd theme, use 'pip install sphinx_rtd_theme'

 doc/conf.py |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/doc/conf.py b/doc/conf.py
index 96eef1c..52514c9 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -120,7 +120,7 @@ todo_include_todos = False
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
 #
-html_theme = 'default'
+html_theme = 'sphinx_rtd_theme'
 
 html_context = {
     'css_files': [