Don't use "with licenses;" for single licences

And don't use square brackets on such lines.

pkgs/tools/misc/t/default.nix

@@ -11,7 +11,7 @@ bundlerEnv {
   meta = with lib; {
     description = "A command-line power tool for Twitter";
     homepage    = http://sferik.github.io/t/;
-    license     = with licenses; asl20;
+    license     = licenses.asl20;
     maintainers = with maintainers; [ offline ];
     platforms   = platforms.unix;
   };