Fix the working directory for the second git command (execute it in git...

Fix the working directory for the second git command (execute it in git repository, like the first command)

gitchart.py

@@ -104,7 +104,8 @@ class GitChart(object):
             proc1 = subprocess.Popen(command1, stdout=subprocess.PIPE,
                                      cwd=self.repository)
             proc2 = subprocess.Popen(command2, stdin=proc1.stdout,
-                                     stdout=subprocess.PIPE)
+                                     stdout=subprocess.PIPE,
+                                     cwd=self.repository)
             proc1.stdout.close()
             return proc2.communicate()[0].decode('utf-8', errors='ignore') \
                 .strip().split('\n')