[skip ci] Update contribution guide

tedium-bot · tedium-bot · commit 444102ca23bf · 2016-05-17T15:33:02.000-07:00
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
@@ -1,4 +1,3 @@
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@@ -11,6 +10,7 @@ specific element:
 
 jsbin=https://jsbin.com/cagaye/edit?html,output
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 # Polymer Elements
 ## Guide for Contributors
 
