Correct the path resolving of the `@extended` documentation (#3847) (#3848)
Correct the path resolving of the `@extended` documentation (#3847) (#3848)

* Correct the path resolving of the `@extended` documentation (#3847)

* Replace string concatenation by a `path.join()`

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