[StGit BUG/PATCH] config.py: fix unset

From: Chris Packham <redacted>

Missing invocation of .run() so config.unset('blah') didn't do anything.
Consequently the fact that the next line set the value to 'None' instead of a
list with 1 element i.e. '[None]' was not noticed.

Signed-off-by: Chris Packham <redacted>
---
 stgit/config.py |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/stgit/config.py b/stgit/config.py
index 4a6cb3b..6f84b10 100644
--- a/stgit/config.py
+++ b/stgit/config.py

@@ -94,8 +94,8 @@ class GitConfig:

        self.__cache[name] = value

    def unset(self, name):
-        Run('git', 'config', '--unset', name)
-        self.__cache[name] = None
+        Run('git', 'config', '--unset', name).run()
+        self.__cache[name] = [None]

    def sections_matching(self, regexp):
        """Takes a regexp with a single group, matches it against all