Update build settings for Travis CI

Hi, thank you very much for this useful library.
I've made some minor fixes regarding setting for Travis CI. So I would like you to take a look at this.

### 1.cocoapods errors

`pod install` is failed as the following log indicates:

````
$ pod install
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:777:in `report_activate_error': Could not find RubyGem cocoapods (>= 0) (Gem::LoadError)
	from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:211:in `activate'
	from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:1056:in `gem'
	from /usr/bin/pod:18
The command "pod install" failed. Retrying, 2 of 3.
````

I added workaround for missing cocoapods. It seems that this is because the mac vm of travis is misconfigured.
See the link for the datails: https://github.com/travis-ci/travis-ci/issues/1657#issuecomment-29045957

### 2. xcodebuild error

After resolved cocoapods failure, then `xcodebuild` is failed as the following log indicates:

````
/Applications/Xcode.app/Contents/Developer/Tools/RunUnitTests:44: error: RunUnitTests is obsolete. To run unit tests for your target, use the Test scheme action in the Xcode IDE and the test action in xcodebuild.
/Applications/Xcode.app/Contents/Developer/Tools/RunUnitTests:45: note: You can remove the Run Script build phase that invokes RunUnitTests from your unit test bundle target.
** BUILD FAILED **
````

`xcodebuild` options is updated on xcode 5. So I updated these options a bit. 
See the link for details: http://stackoverflow.com/questions/18953044/rununittests-error-after-xcode-5-update

### appendix: build & test result

Original: https://travis-ci.org/tumblr/TMTumblrSDK/builds/18420072
Fixed: https://travis-ci.org/honishi/TMTumblrSDK/builds/18567568