Rename the separator kwarg to _separator in StringCommand.

This isn't actually in use currently but shouldn't be a "public" argument
as this means it clashes with the global arguments.

Author: Fizzadar

pyinfra/api/command.py

@@ -73,7 +73,7 @@ class StringCommand(PyinfraCommand):
     def __init__(self, *bits, **kwargs):
         super(StringCommand, self).__init__(**kwargs)
         self.bits = bits
-        self.separator = kwargs.pop('separator', ' ')
+        self.separator = kwargs.pop('_separator', ' ')
 
     def __str__(self):
         return self.get_masked_value()