Force using a version of tls older than 2

This fixes the issue of getting the following error while downloading
package list:

    InternalException (HandshakeFailed (Error_Protocol "peer does not support Extended Main Secret" HandshakeFailure))

elm.cabal

@@ -229,6 +229,7 @@ Executable elm
         snap-server,
         template-haskell,
         time,
+        tls < 2,
         unordered-containers,
         utf8-string,
         vector,