Update Gemspec to allow resque >= 1.25.2

[darrenterhune]

I currently can't use this gem with newer versions of resque. Rolling back our resque gem seems slightly silly just to support resque-rollbar since we already have redis failure setup. I don't see any reason this wouldn't work just fine with the newer release of resque

[syrnick]

Hi @darrenterhune, would you mind to open a pull request? I think, the idea behind that was to lock it to 1.x.x and we haven't tested this beyond 1.25.0 (likely because of this lock).

[darrenterhune]

@syrnick ya I can do that. I'll try and get to it this week, if not the weekend for sure.