fix: Fixed Error: Cannot find module 'regenerator-runtime' (#591)

* fix: Fixed `Error: Cannot find module 'regenerator-runtime'` when `web-ext` was installed using npm 2

* fix: add babel-runtime as prod dep

package.json

@@ -46,6 +46,7 @@
   "dependencies": {
     "addons-linter": "0.15.5",
     "babel-polyfill": "6.16.0",
+    "babel-runtime": "6.11.6",
     "bunyan": "1.8.2",
     "debounce": "1.0.0",
     "es6-error": "4.0.0",
@@ -56,6 +57,7 @@
     "minimatch": "3.0.3",
     "mz": "2.4.0",
     "node-firefox-connect": "1.2.0",
+    "regenerator-runtime": "0.9.5",
     "sign-addon": "0.2.0",
     "source-map-support": "0.4.5",
     "stream-to-promise": "2.2.0",
@@ -76,7 +78,6 @@
     "babel-plugin-transform-runtime": "6.15.0",
     "babel-preset-es2015": "6.16.0",
     "babel-preset-stage-2": "6.17.0",
-    "babel-runtime": "6.11.6",
     "chai": "3.5.0",
     "conventional-changelog-cli": "1.2.0",
     "conventional-changelog-lint": "1.0.1",