Add missing keywords (#1501)

See: https://docs.npmjs.com/files/package.json#keywords

Fixes:
https://www.npmjs.com/package/graphql#license

Author: IvanGoncharov

package.json

@@ -14,6 +14,10 @@
     "type": "git",
     "url": "http://github.com/graphql/graphql-js.git"
   },
+  "keywords": [
+    "graphql",
+    "graphql-js"
+  ],
   "engines": {
     "node": "6.x || 8.x || >= 10.x"
   },