Uncount new commits triggered by submodule

This happened in opnfvdocs project, which uses submodule to tirgger
automatically empty updates from other projects' changes, Which causes
every patchset/review in gerrit will be counted twice in commits:
    - one in orignal project
    - the other in opnfvdocs

This patch is used to deal with new coming commits.

Change-Id: I2f074410ade7dd8c8e9f638ebb5dc4cd70e2842e
Signed-off-by: Julien <zhang.jun3g@zte.com.cn>

stackalytics/processor/vcs.py

@@ -202,6 +202,10 @@ class Git(Vcs):
                 commit[param[0]] = rec.group(i)
                 i += 1
 
+            # ignore machine/script produced submodule auto updates
+            if commit['subject'] == u'Update git submodules':
+                continue
+
             if not commit['author_email']:
                 # ignore commits with empty email (there are some < Essex)
                 continue