Update dependency @babel/core to v7.6.4 (#176)

Author: renovate[bot]

package.json

@@ -35,7 +35,7 @@
     "postbump": "yarn build:packages"
   },
   "devDependencies": {
-    "@babel/core": "7.6.3",
+    "@babel/core": "7.6.4",
     "@babel/plugin-proposal-object-rest-spread": "7.6.2",
     "@babel/plugin-transform-runtime": "7.6.2",
     "@babel/preset-env": "7.6.3",