ulib/Cfg.fst.config.json: Update executable name

ulib/Cfg.fst.config.json

@@ -1,7 +1,7 @@
 {
   "_comment": "Note: the path below must be the 'uninstalled' path (not in out/) so we can still open ulib interactively even if the library failed to build as a whole (which is usually a time when you want to open it!). You can switch to stage2 too, just also switch the include of ulib.checked below",
 
-  "fstar_exe": "../stage1/dune/_build/default/fstarc-full/main.exe",
+  "fstar_exe": "../stage1/dune/_build/default/fstarc-full/fstarc1_full.exe",
   "options": [
     "--ext", "context_pruning",
     "--z3version", "4.13.3"