use assignment in conditionals

As discussed in [this PR](https://github.com/HouseTrip/HouseTrip-Web-App/pull/3370#discussion-diff-6712854) we may want to remove this point :palm_tree:  

![screen shot 2013-10-14 at 13 20 05](https://f.cloud.github.com/assets/1086288/1325469/13165f4c-34cb-11e3-972a-1ee3d704fc98.png)