Check browser specific code.

[davidlehn]

lib/index.js has some browser specific behavior related to a host param. This code makes no difference in the tests. Either the code can be removed or tests should ensure it's working as expected.

[dlongley]

This is the code referenced:

https://github.com/digitalbazaar/http-signature-zcap-invoke/blob/v6.0.0/lib/index.js#L147-L150