fix `miniwdl configure --cfg JUST_FILENAME (#813)

Partially addresses #805

Author: Wid-L-Hacker

WDL/CLI.py

@@ -1850,7 +1850,8 @@ def yes(prompt):
         print(cfg_content)
         print()
         sys.stdout.flush()
-        os.makedirs(os.path.dirname(cfg), exist_ok=True)
+        if dn := os.path.dirname(cfg):
+            os.makedirs(dn, exist_ok=True)
         with open(cfg, "w") as outfile:
             print(
                 f"# miniwdl configure {miniwdl_version or '(version unknown)'} {datetime.utcnow()}Z",