Revise Babel packages

It turns out that some of Babel packages are not used, and others are
transient dependencies and could be omitted. In order to be super clear
about what's going on, let's keep in package.json only those which are
required by the project.

Author: ikalnytskyi

package-lock.json

@@ -46,11 +46,9 @@
     "redux-thunk": "^2.2.0"
   },
   "devDependencies": {
-    "babel-cli": "^6.26.0",
-    "babel-eslint": "^8.0.1",
-    "babel-jest": "^22.0.4",
-    "babel-loader": "^7.1.2",
-    "babel-preset-env": "^1.6.1",
+    "babel-core": "^6.26.3",
+    "babel-loader": "^7.1.4",
+    "babel-preset-env": "^1.7.0",
     "babel-preset-react": "^6.24.1",
     "clean-webpack-plugin": "^0.1.17",
     "cross-env": "^5.1.3",