Update Doc build for split off of 3.7 branch
diff --git a/Doc/tools/extensions/pyspecific.py b/Doc/tools/extensions/pyspecific.py
index 00acd4f..5cb9f1d 100644
--- a/Doc/tools/extensions/pyspecific.py
+++ b/Doc/tools/extensions/pyspecific.py
@@ -35,7 +35,7 @@
 
 
 ISSUE_URI = 'https://bugs.python.org/issue%s'
-SOURCE_URI = 'https://github.com/python/cpython/tree/master/%s'
+SOURCE_URI = 'https://github.com/python/cpython/tree/3.7/%s'
 
 # monkey-patch reST parser to disable alphabetic and roman enumerated lists
 from docutils.parsers.rst.states import Body