Replace hardcoded `localhost` in spec helper.
Replace hardcoded `localhost` in spec helper.

This test had a hardcoded values for the URI to visit which varies for different test cases. When these specs are integrated in custom driver's test suite like capybara-mechanize, it leads to failures.

This replaces #1227, which was rejected for changing the original purpose of the test. However, this patch only changes the hardcoding. It will allow https://github.com/jeroenvandijk/capybara-mechanize/issues/55 to proceed and bump it's compatibility to beyond capybara 2.1.

jillianrosile/capybara,khaidpham/capybara,gonzedge/capybara,mohanraj1311/capybara,khaidpham/capybara,randoum/capybara,shepmaster/capybara,randoum/capybara,ksmaheshkumar/capybara,twalpole/capybara,pombredanne/capybara,irfanah/capybara,y-yagi/capybara,pombredanne/capybara,Bartuz/capybara,olivierlacan/capybara,shepmaster/capybara,Bartuz/capybara,ksmaheshkumar/capybara,olivierlacan/capybara,jnicklas/capybara,ksmaheshkumar/capybara,teamcapybara/capybara,sideci-sample/sideci-sample-capybara,ngpestelos/capybara,ngpestelos/capybara,pombredanne/capybara,sideci-sample/sideci-sample-capybara,olivierlacan/capybara,tjgrathwell/capybara,irfanah/capybara,y-yagi/capybara,khaidpham/capybara,gonzedge/capybara,gonzedge/capybara,irfanah/capybara,mlarraz/capybara,mohanraj1311/capybara,ducthanh/capybara,shepmaster/capybara,twalpole/capybara,jnicklas/capybara,twalpole/capybara,soutaro/capybara,randoum/capybara,tjouan/capybara,teamcapybara/capybara,jnicklas/capybara,ngpestelos/capybara,tjgrathwell/capybara,jillianrosile/capybara,mlarraz/capybara,DariaKalynovska/capybara,DariaKalynovska/capybara,y-yagi/capybara,DariaKalynovska/capybara,ducthanh/capybara,tjouan/capybara,ducthanh/capybara,tjouan/capybara,teamcapybara/capybara,soutaro/capybara,mlarraz/capybara,mohanraj1311/capybara,Bartuz/capybara,tjgrathwell/capybara,jillianrosile/capybara,soutaro/capybara