Move core-js to peerDep (#101)

Author: tizmagik

package-lock.json

@@ -49,11 +49,11 @@
   ],
   "homepage": "https://github.com/NYTimes/react-tracking",
   "dependencies": {
-    "core-js": "2.x",
     "deepmerge": "^2.2.1",
     "hoist-non-react-statics": "^3.0.1"
   },
   "peerDependencies": {
+    "core-js": "2.x",
     "react": "^15.0.0 || ^16.0.0",
     "prop-types": "^15.x"
   },