only apply rewire plugin when running karma tests

.babelrc

 {
   "presets": [["latest", { "es2015": { "modules": false } }], "stage-2"],
   "env": {
-    "development": {
+    "karma": {
       "plugins": ["rewire"]
     },
     "coverage": {

package.json

@@ -5,9 +5,9 @@
     "eslint": "eslint --max-warnings 0 --ext .js,.vue .",
     "eslint-fix": "eslint --max-warnings 0 --ext .js,.vue --fix .",
     "eslint-report": "eslint --max-warnings 0 --ext .js,.vue --format html --output-file ./eslint-report.html .",
-    "karma": "karma start --single-run true config/karma.config.js",
+    "karma": "BABEL_ENV=karma karma start --single-run true config/karma.config.js",
     "karma-coverage": "BABEL_ENV=coverage karma start --single-run true config/karma.config.js",
-    "karma-start": "karma start config/karma.config.js",
+    "karma-start": "BABEL_ENV=karma karma start config/karma.config.js",
     "prettier-staged": "node ./scripts/frontend/prettier.js",
     "prettier-staged-save": "node ./scripts/frontend/prettier.js save",
     "prettier-all": "node ./scripts/frontend/prettier.js check-all",