Adds visbilityjs lib

package.json

@@ -35,6 +35,7 @@
     "stats-webpack-plugin": "^0.4.3",
     "timeago.js": "^2.0.5",
     "underscore": "^1.8.3",
+    "visibilityjs": "^1.2.4",
     "vue": "^2.2.4",
     "vue-resource": "^0.9.3",
     "webpack": "^2.2.1",

yarn.lock

@@ -4450,6 +4450,10 @@ verror@1.3.6:
   dependencies:
     extsprintf "1.0.2"
 
+visibilityjs@^1.2.4:
+  version "1.2.4"
+  resolved "https://registry.yarnpkg.com/visibilityjs/-/visibilityjs-1.2.4.tgz#bff8663da62c8c10ad4ee5ae6a1ae6fac4259d63"
+
 vm-browserify@0.0.4:
   version "0.0.4"
   resolved "https://registry.yarnpkg.com/vm-browserify/-/vm-browserify-0.0.4.tgz#5d7ea45bbef9e4a6ff65f95438e0a87c357d5a73"