Auto merge of #715 - jrmuizel:shader-changes, r=kvark
Auto merge of #715 - jrmuizel:shader-changes, r=kvark

Make sure we track shader changes in build.rs

rerun-if-changed is not recursive so we need to make sure that
we output directive for all of the files as well as the directory

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servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender