[INTERNAL] Have greenkeeper-lockfile amend any greenkeeper commit

Otherwise it would use a non-configurable commit message that differs
from our msg style

.travis.yml

@@ -15,4 +15,5 @@ after_script:
 
 env:
   global:
-    secure: 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
+    - GK_LOCK_COMMIT_AMEND: true
+    - secure: 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