switch to node-fetch (#2587)

* switch to node-fetch

* remove useless var declaration

* remove method uppercasing

* rework concurrency

* Revert "rework concurrency"

This reverts commit ef6aa2697e.

* fix headers

package.json

@@ -34,9 +34,10 @@
   "runkitExampleFilename": "./docs/examples/ping.js",
   "unpkg": "./webpack/discord.min.js",
   "dependencies": {
+    "form-data": "^2.3.2",
+    "node-fetch": "^2.1.2",
     "pako": "^1.0.0",
     "prism-media": "^0.2.0",
-    "snekfetch": "^3.6.0",
     "tweetnacl": "^1.0.0",
     "ws": "^4.0.0"
   },