Remove type: "commonjs" to fix importing in NextJS

When `"type": "commonjs"` is specified in our package.json, it
apparently causes the following problem in NextJS:

```
Module parse failed: 'import' and 'export' may appear only with 'sourceType: module' (1:0)
> export { default as ControlledBubbleMenu, } from "./ControlledBubbleMenu";
| export { default as LinkBubbleMenu, } from "./LinkBubbleMenu";
| export { default as MenuBar } from "./MenuBar";
```

This is odd, since we indeed *are* using "commonjs" type, as that's the
default, but it seems that fortunately merely omitting this resolves
import errors in NextJS, and still supports NodeJS.

Should resolve #264,
removing one of the changes from
#259, while still
hopefully keeping #256
fixed.

package.json

@@ -21,7 +21,6 @@
   "files": [
     "dist"
   ],
-  "type": "commonjs",
   "types": "./dist/cjs/index.d.ts",
   "main": "dist/cjs/index.js",
   "module": "dist/esm/index.js",