Fix datetime parsing on python 3.5

datetime.astimezone supports native datetimes only since python 3.6

fixes #162

toot/tui/utils.py

@@ -2,7 +2,7 @@
 import shutil
 import subprocess
 
-from datetime import datetime
+from datetime import datetime, timezone
 
 HASHTAG_PATTERN = re.compile(r'(?<!\w)(#\w+)\b')
 
@@ -13,7 +13,7 @@ def parse_datetime(value):
     # In Python < 3.7, `%z` does not match `Z` offset
     # https://docs.python.org/3.7/library/datetime.html#strftime-and-strptime-behavior
     if value.endswith("Z"):
-        dttm = datetime.strptime(value, "%Y-%m-%dT%H:%M:%S.%fZ")
+        dttm = datetime.strptime(value, "%Y-%m-%dT%H:%M:%S.%fZ").replace(tzinfo=timezone.utc)
     else:
         dttm = datetime.strptime(value, "%Y-%m-%dT%H:%M:%S.%f%z")