Add YAML as an explicit dependency of CocoaPodUI

[guillaumealgis]

This makes possible to build the plugin with xcodebuild.

Previously, the build would fail with

clang: error: no such file or directory: '/tmp/cocoapodui-build/Release/YAML.framework/YAML'

After adding the YAML library as a dependency, the plugin compiles fine with the command line.

This is probably somewhat related to #18