fix: Move babel-core to devDependencies

This was added to dependencies when it was supposed to have been added to devDependencies.

Fixes #146.

package.json

@@ -15,7 +15,6 @@
   "maintainers": ["Simon Fridlund <[email protected]>"],
   "license": "MIT",
   "dependencies": {
-    "babel-core": "6.26.0",
     "common-tags": "^1.4.0",
     "dlv": "^1.1.0",
     "eslint": "^4.5.0",
@@ -31,6 +30,7 @@
   "devDependencies": {
     "all-contributors-cli": "^4.4.0",
     "babel-cli": "^6.26.0",
+    "babel-core": "6.26.0",
     "babel-jest": "^21.2.0",
     "babel-plugin-transform-class-properties": "6.24.1",
     "babel-plugin-transform-object-rest-spread": "6.26.0",