Add buildx history command

These commands allow working with build records
of completed and running builds.

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/github.com/pkg/browser/browser_darwin.go

@@ -0,0 +1,5 @@
+package browser
+
+func openBrowser(url string) error {
+	return runCmd("open", url)
+}