git.py: Parse timestamps from UTC, not from local time

The current parsing of dates from git incorrectly uses
datetime.fromtimestamp(), which returns the *local* date and time
corresponding to the given timestamp.

Instead, it should be using datetime.utcfromtimestamp() which returns the UTC
date and time, as the rest of the code expects.

Signed-off-by: Alberto Bertogli <albertito@blitiri.com.ar>

git.py

@@ -452,7 +452,7 @@ class Date:
     def __init__(self, epoch, tz):
         self.epoch = int(epoch)
         self.tz = tz
-        self.utc = datetime.datetime.fromtimestamp(self.epoch)
+        self.utc = datetime.datetime.utcfromtimestamp(self.epoch)
 
         self.tz_sec_offset_min = int(tz[1:3]) * 60 + int(tz[4:])
         if tz[0] == '-':