Switch to using npm over yarn

Signed-off-by: Janne Savolainen <janne.savolainen@live.fi>

packages/node-fetch/package.json

@@ -18,8 +18,8 @@
     "build": "webpack --config webpack.ts",
     "lint": "exit 0",
     "prepare": "npm run build",
-    "prepare:dev": "yarn run build",
-    "prepare:test": "yarn run build"
+    "prepare:dev": "npm run build",
+    "prepare:test": "npm run build"
   },
   "dependencies": {
     "node-fetch": "^3.3.0",