Fixed mobile chrome bug for rich text editor

This PR modifies Gemfile to point bootstrap-wisihtml5 gem installation to my git repo. 

Previous check IOS function: 
1. Check whether it is webkit and 
2. Check IOS version to be greater than 0. 
=> Chrome mobile fails these two checks despite it not being IOS. 

New gem rectifies the check IOS function and allows mobile chrome to work.

I will submit the suggested change to original open source git repo. If they accept my changes, we can rectify gemfile to point back to original gem.