Fix style in Presubmit.py

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@11715 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index b86bc146..7cb4af3 100755
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -9,7 +9,7 @@
 details on the presubmit API built into gcl.
 """
 
-# Files with these extensions will be considered source files
+# Files with these extensions will be considered source files.
 SOURCE_FILE_EXTENSIONS = [
     '.c', '.cc', '.cpp', '.h', '.m', '.mm', '.py', '.mk', '.am', '.json',
 ]