_content/blog: fix unavailable link

_content/blog/go12.md

@@ -39,7 +39,7 @@ package.
 A major new feature of the tool chain is the facility to compute and display
 [test coverage results](/doc/go1.2#cover).
 See the [`go test`](/cmd/go/#hdr-Description_of_testing_flags)
-and [cover tool](https://pkg.go.dev/golang.org/x/tools/cover)
+and [cover tool](https://golang.org/x/tools/cmd/cover)
 documentation for details. Later this week we will publish an article that
 discusses this new feature in detail.