plugins/lsp: use attrsOf anything instead of attrs for extraOptio…

…ns (nix-community#1235)

`attrs` is not merged correctly, this can introduce conflicts with
efmls-configs for example when trying to register `efm` sources not
defined by efmls-configs.

plugins/lsp/helpers.nix

@@ -77,7 +77,7 @@
 
           extraOptions = mkOption {
             default = {};
-            type = types.attrs;
+            type = types.attrsOf types.anything;
             description = "Extra options for the ${name} language server.";
           };
         };