Add missing dependencies.

Author: chrsep

package.json

@@ -8,6 +8,8 @@
   },
   "dependencies": {
     "@babel/runtime": "^7.4.5",
+    "@formatjs/intl-pluralrules": "^1.3.1",
+    "@formatjs/intl-relativetimeformat": "^4.2.1",
     "browser-lang": "^0.1.0",
     "intl": "^1.2.5",
     "react-intl": "^3.4.0"