internal/links: improve links parser, no protocol specification
internal/links: improve links parser, no protocol specification

The existing implementation has no consideration of links with no
protocol specification, so "example.com/comments" now it's trated as
"https://example.com/comments"

"Fixes golang/go#33505"

Corrects the regexp definition

Change-Id: I587d611f26a3f3c5ea89eda7b2c3ccf369e8bb2f
GitHub-Last-Rev: 740ffca04dd16b36a96f03781d58ff727e39ae79
GitHub-Pull-Request: golang/tools#154
Reviewed-on: https://go-review.googlesource.com/c/tools/+/194661
Reviewed-by: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools