Fix tests for OS X machines with IPv6 enabled.

The tests are currently failing hard on my mac, lots of connection refused errors:

    t/01-load-debugger-html.t ......... Can't get debugger gui': Can't connect to localhost:62106 (Connection refused)    # Child (Main debugger page) exited without calling finalize()

Changing the url from localhost to 127.0.0.1 fixed the test suite for me.