Removing one of two instances of 'rake' in Gemfile

[L2G]

I was getting weary of seeing this message every time I ran Bundler:

Your Gemfile lists the gem rake (>= 0) more than once.
You should probably keep only one of them.
While it's not a problem now, it could cause errors if you change the version of just one of them later.

Rake is included both in the main list of gems and in the development group. I opted to remove it from the development group since I believe admins as well as developers will want to be able to run some Rake tasks.

[coveralls]

Coverage remained the same when pulling 91b9b4d on L2G:redundant-rake into 638248b on cantino:master.

[cantino]

Oops. Thanks :)