Add gsutil.vpython spec to recipe bundles

Bug: 764673
Change-Id: I8cb5c95cccfa0afbea441a85b062de48c185af19
Reviewed-on: https://chromium-review.googlesource.com/665121
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Daniel Jacques <dnj@chromium.org>

.gitattributes

@@ -9,6 +9,9 @@
 /*.py  recipes
 /*.sh  recipes
 
+# vpython specs
+/gsutil.vpython recipes
+
 # Extensionless tools we want and support scripts.
 /apply_issue                  recipes
 /clang*                       recipes