Also parse js.flow files with hermes-parser (facebook#39048)

Summary:
Pull Request resolved: facebook#39048

Similar to D48047348, we should also use hermes-parser to parse .js.flow files to support newer Flow syntax.

Changelog: [Internal]

Reviewed By: yungsters

Differential Revision: D48398780

fbshipit-source-id: 280ac546493361c4421449f86bf3f735b93a18e8

Author: SamChou19815

.prettierrc

@@ -9,7 +9,8 @@
   "overrides": [
     {
       "files": [
-        "*.js"
+        "*.js",
+        "*.js.flow"
       ],
       "options": {
         "parser": "hermes"