Follow PEP 0394 and use /usr/bin/env python so that the python in the
users venv is respected. Not that the kitty python files are meant to be
executed standalone anyway, but, whatever.
Fixes#6810
Without this fix the file with the list of notifications looks like this:
```
0.19.0,1601899026.4373078,<built-in method count of Notification object at 0x7f8c582193b0>
```
which ends up notifying about a new version all the time.
According to the text just above https://docs.python.org/3/library/exceptions.html#EnvironmentError, `EnvironmentError` has been an alias of `OSError` since Python 3.3. Replacing it makes the code more consistent since `OSError` is used in other places in the code too.
Using
```Python
with suppress(OSError):
os.remove('somefile.tmp')
```
instead of
```Python
try:
os.remove('somefile.tmp')
except OSError:
pass
```
makes the code more compact and more readable IMO.
This pattern was recommended by Raymond Hettinger, a Python Core
Developer in his talk "Transforming Code into Beautiful, Idiomatic Python" at https://www.youtube.com/watch?v=OSGv2VnC0go. The transcript is available at https://github.com/JeffPaine/beautiful_idiomatic_python
