owamp: use insecure livecheck URL to make the misconfigured server happy

Ref: https://github.com/Homebrew/homebrew-core/pull/60334#issuecomment-688133722

Formula/owamp.rb

@@ -6,7 +6,8 @@ class Owamp < Formula
   license "Apache-2.0"
 
   livecheck do
-    url "https://software.internet2.edu/sources/owamp/"
+    # HTTP allows directory listing while HTTPS returns 403
+    url "http://software.internet2.edu/sources/owamp/"
     regex(/href=.*?owamp[._-]v?(\d+(?:\.\d+)+(?:-\d+)?)\.t/i)
   end