Notify Intercom of URL changes in SPAs

[GeKorm]

From the Intercom docs

For single paged apps or pages where the URL changes without a full page reload, the Intercom Messenger does not automatically send URL changes to Intercom to match messages based on URLs. You will need to call Intercom("update") in order to initiate a "ping" every time a URL changes.

Without this, Intercom won't be able to track page views correctly, or dispatch automated messages based on URL triggers.

@nhagen :)

[nhagen]

Thanks for this PR--this should have been addressed sooner than now. This should be addressed by v2.0.0-alpha.1 and #73, since update is called every time props change.