Empty URL args make GTM fail to load.

[yasiupl]

When using just GTM ID to initialize the plugin, the empty tags included in the URL cause it to fail to load.

Example:
https://www.googletagmanager.com/gtm.js?id=GTM-PBBB4LF&l=&gtm_auth=&gtm_preview=&gtm_cookies_win=x

vs.

https://www.googletagmanager.com/gtm.js?id=GTM-PBBB4LF

[yasiupl]

Looks like it's just the "x" at the end that breaks it. Can it be removed?

[yasiupl]

It's actually the empty &l= tag added when dataLayerName is not specified.

[yasiupl]

PR #3

[ayr-ton]

@yasiupl This one is inactive for a while. I've started a webpack5 fork with dependencies updates and merged your PR as it was not approved here.