fix: Use window.location.pathname if anchor pathname is empty (IE11)

[cluick]

IE11 will return an empty pathname for anchors where the href attribute contains a relative link consisting of only a query parameter (e.g. "?search=test"). This will not fix cases where the relative link contains a relative path (e.g. "foo/bar.html").

[coveralls]

Coverage remained the same at 90.449% when pulling 63957ed9720a463073e71a7ea98bd1d2518a7eb4 on cluick:master into 043e68cfdea0c8adec24c4e719c4af2c956b96e0 on visionmedia:master.