gem-config: add semian

Note: on macOS, it works without this config. Testing on Ubuntu/Debian with the parent sha will produce an error about extconf.rb failing to find openssl/sha.h.

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

@@ -358,6 +358,10 @@ in
       '';
     } else {};
 
+  semian = attrs: {
+    buildInputs = [ openssl ];
+  };
+
   sequel_pg = attrs: {
     buildInputs = [ postgresql ];
   };