test: expand test coverage for url.js

Currently, line 156 of lib/url.js is not reachable from test-url because
there is no example URL which has a white space in the front of the url.
I added one example which can reach that line.

PR-URL: https://github.com/nodejs/node/pull/8859


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ilkka Myller <ilkka.myller@nodefield.com>
Reviewed-By: Franziska Hinkelmann <fhinkel@vt.edu>