Bump babel to 7 beta.54

Summary:
@public
Bump Babel to version 7 beta 54

This version has reversed the windows path denormalization so we need it to be able to fix windows paths.

Reviewed By: rafeca

Differential Revision: D8894700

fbshipit-source-id: 3ae1480b77380cae8070621d4729b21a34c4b928

package.json

@@ -199,7 +199,7 @@
     "yargs": "^9.0.0"
   },
   "devDependencies": {
-    "@babel/core": "7.0.0-beta.48",
+    "@babel/core": "7.0.0-beta.54",
     "async": "^2.4.0",
     "babel-eslint": "9.0.0-beta.2",
     "babel-generator": "^6.26.0",