elmPackages.lamdera: homepage from URL literal to string

reported by @ajs124
> this breaks nixpkgs.tarball on unstable-small, because of the url literal

This should address the issue

pkgs/development/compilers/elm/packages/lamdera.nix

···
   '';
 
   meta = with lib; {
-    homepage = https://lamdera.com;
+    homepage = "https://lamdera.com";
     license = licenses.unfree;
     description = "A delightful platform for full-stack web apps";
     platforms = [ "x86_64-linux" ];