preventing errors when scoped custom element registry is imported on the server

[jonathandewitt-dev]

Fixes #601

This will log a warning when imported on the server, and it will effectively do nothing. Otherwise, it will carry on as the polyfill usually would for browser environments.

NOTE: make sure to enable "hide whitespace."

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[jonathandewitt-dev]

I have signed the CLA, not sure why it's failing... maybe it's an issue with my git config.

EDIT: got it. It was indeed an issue with my git config. A little rewriting history with a new email fixed it.

[jonathandewitt-dev]

I'll add changelog updates when I get home too.

[jonathandewitt-dev]

Closing as not needed. See https://github.com/webcomponents/polyfills/issues/601 for details.