Update nmodl submodule to latest release 0.3 (#534)

Nicolas Cornu · web-flow · commit 1f27c839f944 · 2021-04-28T20:51:21.000+02:00
diff --git a/external/nmodl b/external/nmodl
@@ -1 +1 @@
-Subproject commit dcaf303566bf4a183cf667e31a45a680c7a006fe
+Subproject commit 39cdaf4c74d5a448fd4e1dd0c4037db76f3abbdd
