Release v0.5.0 (#98)

diff --git a/docs/conf.py b/docs/conf.py
index 140fe51..b045c8c 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -13,6 +13,8 @@
 # All configuration values have a default; values that are commented out
 # serve to show the default.
 
+import pkg_resources
+
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use os.path.abspath to make it absolute, like shown here.
@@ -64,9 +66,9 @@
 # built documents.
 #
 # The short X.Y version.
-version = '0.4.0'
+version = pkg_resources.get_distribution('google-auth').version
 # The full version, including alpha/beta/rc tags.
-release = '0.4.0'
+release = version
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.