Use another augmented assignment statement

[elfring]

:eyes: Some source code analysis tools can help to find opportunities for improving software components. :thought_balloon: I propose to increase the usage of augmented assignment statements accordingly.

diff --git a/fire/core.py b/fire/core.py
index 8ca142c..67b1c72 100644
--- a/fire/core.py
+++ b/fire/core.py
@@ -570,7 +570,7 @@ def _Fire(component, args, parsed_flag_args, context, name=None):
     if used_separator:
       # Add back in the arguments from after the separator.
       if remaining_args:
-        remaining_args = remaining_args + [separator] + saved_args
+        remaining_args += [separator] + saved_args
       elif (inspect.isclass(last_component)
             or inspect.isroutine(last_component)):
         remaining_args = saved_args