Change "browser" to "unpkg" in package.json. (#173)

* change browser => npm

* spell things right.

Author: Nikhil Thorat

package.json

@@ -4,7 +4,7 @@
   "description": "Hardware-accelerated JavaScript library for machine intelligence",
   "private": false,
   "main": "dist/src/index.js",
-  "browser": "dist/deeplearn.js",
+  "unpkg": "dist/deeplearn.js",
   "types": "dist/src/index.d.ts",
   "repository": {
     "type": "git",