gem-config: add snappy

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

@@ -21,8 +21,8 @@
 , libiconv, postgresql, v8_3_16_14, clang, sqlite, zlib, imagemagick
 , pkgconfig , ncurses, xapian, gpgme, utillinux, fetchpatch, tzdata, icu, libffi
 , cmake, libssh2, openssl, mysql, darwin, git, perl, gecode_3, curl
-, libmsgpack, qt48, libsodium
-}:
+, libmsgpack, qt48, libsodium, snappy
+}@args:
 
 let
   v8 = v8_3_16_14;
@@ -145,6 +145,10 @@ in
     buildInputs = [ cmake pkgconfig openssl libssh2 zlib ];
   };
 
+  snappy = attrs: {
+    buildInputs = [ args.snappy ];
+  };
+
   sqlite3 = attrs: {
     buildFlags = [
       "--with-sqlite3-include=${sqlite.dev}/include"