🤖 chore: Add cover key in .babel.env.

These changes were automatically generated by a transform whose code can be found at:
  - https://github.com/make-github-pseudonymous-again/rejuvenate/blob/7a92df9c28303ed9cd6ee1a5e4999acfc8c52497/src/transforms/package.json:ensure-babel-env-cover.js
Please contact the author of the transform if you believe there was an error.

package.json

@@ -143,6 +143,7 @@
           ]
         ]
       },
+      "cover": {},
       "development": {
         "presets": [
           "babel-preset-power-assert"