Fix order of operators before executing the git command

Since Python 3.3, the hash value of an object is seeded randomly, making it
change between each call. As a consequence, the `dict` type relying on the hash
value for the order of the items upon iterating on it, and the parameters
passed to `git` being passed as `kwargs` to the `execute()` method, the order
of parameters will change randomly between calls.

For example, when you call `git.remote.pull()` in a code, two consecutives run
will generate:

1. git pull --progress -v origin master
2. git pull -v --progress origin master

By simply adding the `sorted()` call around `args` within the `transform_kwargs()`
method, it will ensure that each subsequent calls will execute the parameters in
the same order.

git/cmd.py

@@ -789,7 +789,7 @@ def transform_kwargs(self, split_single_char_options=True, **kwargs):
                     args += self.transform_kwarg(k, value, split_single_char_options)
             else:
                 args += self.transform_kwarg(k, v, split_single_char_options)
-        return args
+        return sorted(args)
 
     @classmethod
     def __unpack_args(cls, arg_list):