chore(package): update image-webpack-loader to version 5.1.0

Closes #214

Author: greenkeeper[bot]

package.json

@@ -23,7 +23,7 @@
     "git-prepush-hook": "^1.0.1",
     "html-loader": "^0.5.5",
     "html-webpack-plugin": "^3.0.0",
-    "image-webpack-loader": "^4.0.0",
+    "image-webpack-loader": "^5.1.0",
     "jsdom": "^11.6.2",
     "json-loader": "^0.5.7",
     "manifest-scope-loader": "^1.0.1",