Fix standard linting
Fix standard linting

Fixes the following linting errors:

```
standard: Use JavaScript Standard Style (https://standardjs.com)
  /Users/linus/coding/standard/tmp/instant.io/client/index.js:261:25: 'URL' is not defined. (no-undef)
  /Users/linus/coding/standard/tmp/instant.io/client/index.js:267:17: 'URL' is not defined. (no-undef)
```
jhiesey/instant.io,jhiesey/instant.io,feross/instant.io,feross/instant.io,jhiesey/instant.io,feross/instant.io