ruby-modules/gem-config: add readline-ext

This is needed because redline-ext references the libreadline library and readline-ext is used by evil-winrm

pkgs/development/ruby-modules/gem-config/default.nix

@@ -42,6 +42,7 @@
   xapian,
   gpgme,
   util-linux,
+  readline,
   tzdata,
   icu,
   libffi,
@@ -962,6 +963,10 @@ in
     ];
   };
 
+  readline-ext = attrs: {
+    buildInputs = [ readline ];
+  };
+
   rest-client = attrs: {
     meta.mainProgram = "restclient";
   };