Runtime-host meta tag never tested

[schlessera]

The runtime-host meta tag does not seem to be tested at all, as all the tests use a relative ampUrlPrefix and thus throw an exception in the related code.

amp-toolbox/packages/optimizer/lib/transformers/RewriteAmpUrls.js

Lines 116 to 120 in 3ec7bd4

	try {
	const url = new URL(host);
	this._addMeta(head, 'runtime-host', url.origin);
	} catch (e) {
	this.log.warn('ampUrlPrefix must be an absolute URL');

I assume this is either an oversight or a bug in the tests.