Use time zones for readability

.github/calendar.yml

 {
-  '2018-01-30T02:00Z': 'endgame',
-  '2018-02-07T20:00Z': 'release', # 1.20.0
-  '2018-02-12T20:00Z': 'development',
-  '2018-02-14T15:00Z': 'release', # 1.20.1
-  '2018-02-19T20:00Z': 'development',
-  '2018-02-27T02:00Z': 'endgame',
+  '2018-01-29 18:00, US/Pacific':    'endgame',
+  '2018-02-07 12:00, US/Pacific':    'release', # 1.20.0
+  '2018-02-12 12:00, US/Pacific':    'development',
+  '2018-02-14 16:00, Europe/Zurich': 'release', # 1.20.1
+  '2018-02-19 16:00, Europe/Zurich': 'development',
+  '2018-02-26 18:00, US/Pacific':    'endgame',
 }
\ No newline at end of file