Fix missing reference url slash

[ataylorme]

Addresses #25 by replacing one or more trailing slashes in referenceUrl with a single trailing slash.

[danreeves]

This doesn't solve the issue I had where the URL has a trailing slash and so does the referenceUrl, resulting in two slashes at the end of the domain. Right?

I think it was a mistake on my part to hack around this with a regex. I'd rather fix the url we're placing in the currentScenario with normalize-url. e.g.http://requirebin.com/?gist=b34c314281156c23c0e21dc2dd970c4b

[ataylorme]

@danreeves makes sense to me. I think we will have to be careful as removeTrailingSlash says Note: Trailing slash is always removed if the URL doesn't have a pathname.

This means http://test.com/////// will turn into http://test.com, so we will need to add a trailing slash back.

[danreeves]

If we do at the point where we have the full url, before https://github.com/fffunction/backstop-crawl/blob/master/lib/crawl.js#L116 it should be fine.

[coveralls]

Coverage remained the same at 100.0% when pulling 6d15dba on ataylorme:missing-reference-url-slash into e6ecdd8 on fffunction:master.

[ataylorme]

@danreeves should be all set now. Thanks for talking through this with me!