minor fix to code example.
minor fix to code example.

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