don't build docs if no theme (#3314)
don't build docs if no theme (#3314)


playi/pxt,playi/pxt,playi/pxt,Microsoft/pxt,Microsoft/pxt,switchinnovations/pxt,switch-education/pxt,playi/pxt,switchinnovations/pxt,switch-education/pxt,switchinnovations/pxt,Microsoft/pxt,Microsoft/pxt,switch-education/pxt,switchinnovations/pxt,switch-education/pxt,switch-education/pxt,Microsoft/pxt