Fix dangerous warning about sys.argv as default value

src/shellman/cli.py

@@ -30,7 +30,7 @@
 from .formatter import get_formatter
 
 
-def main(argv=sys.argv):
+def main(argv=None):
     """
     Main function.
 
@@ -45,9 +45,11 @@ def main(argv=sys.argv):
     (default to text), get the according formatter class, instantiate it
     with acquired doc and write on stdout.
     """
+
+    if argv is None:
+        argv = sys.argv[1:]
+
     f = argv[0]
-    if f == sys.argv[0]:
-        f = argv[1]
     doc = Doc(f).read()
     fmt = os.environ.get('SHELLMAN_FORMAT', 'text')
     get_formatter(fmt)(doc).write()