THRIFT-4551: Add Prettier for consistent JS code formatting (#1536)

Client: js
diff --git a/package-lock.json b/package-lock.json
index 27bd5e9..4b16899 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1382,6 +1382,12 @@
       "integrity": "sha1-IZMqVJ9eUv/ZqCf1cOBL5iqX2lQ=",
       "dev": true
     },
+    "prettier": {
+      "version": "1.11.1",
+      "resolved": "https://unpm.uberinternal.com/prettier/-/prettier-1.11.1.tgz",
+      "integrity": "sha512-T/KD65Ot0PB97xTrG8afQ46x3oiVhnfGjGESSI9NWYcG92+OUPZKkwHqGWXH2t9jK1crnQjubECW0FuOth+hxw==",
+      "dev": true
+    },
     "process-nextick-args": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/process-nextick-args/-/process-nextick-args-2.0.0.tgz",