Add xcode formatter to danger

[Palleas]

No description provided.

[SPopenko]

@Palleas I believe you need the minor update for Danger file to let this PR passed danger check.
This line

%x( cat "#{OUTPUT}" | XCPRETTY_JSON_FILE_OUTPUT=xcodebuild_output.json bundle exec xcpretty -f "#{FORMATTER}" )

should be updated to this one:

%x( cat "#{OUTPUT}" | XCPRETTY_JSON_FILE_OUTPUT=xcodebuild_output.json bundle exec xcpretty -f `#{FORMATTER}` )