fix invalid manifest.json
fix invalid manifest.json

trailing comma not allowed
vinitkumar/socialschools-chrome-extension,swerner/mouseflow-demo,davidfurlong/chrome-boilerplate,jaredsohn/hnkarmabreakdown,dmikey/enyo-chrome-extension-bootplate,dmikey/enyo-chrome-extension-bootplate,umair-gujjar/chrome-boilerplate,modulexcite/chrome-boilerplate,danvk/github-syntax,jcblw/gist-clipboard,jaredsohn/hnkarmabreakdown