resolve rtcss/autoprefixer when compiling semantic only (#1984)
resolve rtcss/autoprefixer when compiling semantic only (#1984)


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