Really store UTC time

Calling datetime.datetime.now will produce local time, whereas utcnow will
result with UTC time.

/reviewed-on !2

src/surykatka/db.py

@@ -44,7 +44,7 @@ class LogDB:
                 resolution=6,
                 # date is in UTC
                 utc=True,
-                default=datetime.datetime.now,
+                default=datetime.datetime.utcnow,
             )
 
         # Store the configuration modification