Update dashboard reference from master to main 🧙

This updates any reference of dashboard repository to target the
main branch instead of the master branch.

Signed-off-by: Vincent Demeester <vdemeest@redhat.com>

Author: vdemeester

roadmap.md

@@ -8,7 +8,7 @@ This doc describes Tekton's mission and the 2020 roadmap.
   - [Pipeline](https://github.com/tektoncd/pipeline/blob/master/roadmap.md)
   - [Triggers](https://github.com/tektoncd/triggers/blob/master/roadmap.md)
   - [Catalog](https://github.com/tektoncd/catalog/blob/master/roadmap.md)
-  - [Dashboard](https://github.com/tektoncd/dashboard/blob/master/roadmap.md)
+  - [Dashboard](https://github.com/tektoncd/dashboard/blob/main/roadmap.md)
   - [CLI](https://github.com/tektoncd/cli/blob/master/ROADMAP.md)
 
 ## Mission and Vision