languages/ts: register javascript with prettier formatter (#595)

modules/plugins/languages/ts.nix

@@ -82,7 +82,7 @@
           ls_sources,
           null_ls.builtins.formatting.prettier.with({
             command = "${cfg.format.package}/bin/prettier",
-            filetypes = { "typescript" },
+            filetypes = { "typescript", "javascript" },
           })
         )
       '';