workbench: add graphmod for Cabal dependency support

deepfire · deepfire · commit 1a7097039019 · 2022-08-24T00:53:26.000+08:00
diff --git a/nix/workbench/shell.nix b/nix/workbench/shell.nix
@@ -92,6 +92,7 @@ in project.shellFor {
     ghcid
     haskellBuildUtils
     pkgs.graphviz
+    graphmod
     weeder
     nixWrapped
     pkgconfig
