can't build mac apps with grunt-xcode

[skhavari]

Repro

• fire up xcode 6
• create a new mac app
• build it with xcode, run it make sure it works
• build it with xcodebuild, make sure it works

Expect

• be able to build it with grunt-xcode

Actual

• always fails and never builds the target

perhaps im reading the code wrong or missing something but I don't see any configuration that invokes xcodebuild build, or the build action (according to the xcodebuild man page)