Simplify repository url (#9947)

https://docs.npmjs.com/files/package.json#repository

package.json

@@ -3,6 +3,7 @@
   "version": "0.82.0",
   "description": "JavaScript 3D library",
   "main": "build/three.js",
+  "repository": "mrdoob/three.js",
   "jsnext:main": "build/three.modules.js",
   "files": [
     "package.json",
@@ -28,10 +29,6 @@
     "dev": "rollup -c -w",
     "test": "echo \"Error: no test specified\" && exit 1"
   },
-  "repository": {
-    "type": "git",
-    "url": "https://github.com/mrdoob/three.js"
-  },
   "keywords": [
     "three",
     "three.js",