submit should show link to PR, not just PR number, when updating PRs

[boneskull]

e.g.:

Updating PR #3150 for boneskull/additional-locations (base: master)... ok
Updating PR #3186 for boneskull/async-parser (base: master)... ok

becomes:

Updating PR #3150 (https://github.com/org/repo/pull/3150) for boneskull/additional-locations (base: master)... ok
Updating PR #3186 (https://github.com/org/repo/pull/3186) for boneskull/async-parser (base: master)... ok

The above example shows the fallback implementation; wherever terminal links are available, the text PR #nnnn should be the linked text.