Explicitly define propertyUtils in TapeRepresenter

When trying to run tests from within IntelliJ, I hit the following error:

`groovy.lang.MissingPropertyException: No such property: propertyUtils for class: co.freeside.betamax.tape.yaml.TapeRepresenter`

Per http://undefined.com/ia/2008/03/17/groovy-no-such-property-x-for-class-y/, seems we need to explicitly declare `propertyUtils` as a member of the `TapeRepresenter` class. 

There may be more cases were similar edits need to be made.