chore: release 3.4.0 (#195)

This release only contains updates in debian packaging. All other platforms
could safely continue to use 3.2.0 or 3.3.0.

I didn't want to make a path release, though, because I didn't want to convey
the meaning that something was fixed.

Related to ooni/ooni.org#677

internal/version/version.go

@@ -3,5 +3,5 @@ package version
 
 const (
 	// Version is the software version
-	Version = "3.4.0-alpha"
+	Version = "3.4.0"
 )