Fix a corner case in my_reviews.py's median latency calculation.

Review URL: https://chromiumcodereview.appspot.com/19460002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@211880 0039d316-1c4b-4281-b951-d872f2087c98

my_reviews.py

@@ -86,7 +86,7 @@ class Stats(object):
     length = len(self.latencies)
     latencies = sorted(self.latencies)
     if (length & 1) == 0:
-      return (latencies[length/2] + latencies[length/2+1]) / 2.
+      return (latencies[length/2] + latencies[length/2-1]) / 2.
     else:
       return latencies[length/2]