remove eventsource-polyfill (vuejs-templates#1169)

Author: PanJiaChen

template/package.json

@@ -94,7 +94,6 @@
     "chalk": "^2.0.1",
     "copy-webpack-plugin": "^4.0.1",
     "css-loader": "^0.28.0",
-    "eventsource-polyfill": "^0.9.6",
     "extract-text-webpack-plugin": "^3.0.0",
     "file-loader": "^1.1.4",
     "friendly-errors-webpack-plugin": "^1.6.1",