on-modify.timewarrior: The start command does not accept ranges but only a single datetime.

It seems like the hook script doesn't like it, when a given tag can be read as time/date:

The script works fine without a tag:
```
tasksh> add 'Test Timewarrior'
[task add 'Test Timewarrior']
Created task 302.
tasksh> start 302
[task start 302]
Starting task a36684d6 'Test Timewarrior'.
Started 1 task.
Tracking "Test Timewarrior"
Started 2021-09-24T08:12:10
Current 10
Total 0:00:00
You have more urgent tasks.
tasksh> stop 302
[task stop 302]
Stopping task a36684d6 'Test Timewarrior'.
Stopped 1 task.
Recorded "Test Timewarrior"
Started 2021-09-24T08:12:10
Ended 12
Total 0:00:02
```

Script fails with the tag `today`:
```
tasksh> 302 mod +today
[task 302 mod +today]
Modifying task 302 'Test Timewarrior'.
Modified 1 task.
tasksh> start 302
[task start 302]
The start command does not accept ranges but only a single datetime. Perhaps you want the track command?
Starting task a36684d6 'Test Timewarrior'.
Started 1 task.

tasksh> stop 302
[task stop 302]
There is no active time tracking.
Stopping task a36684d6 'Test Timewarrior'.
Stopped 1 task.
```

Tag `anything` works fine again:
```
tasksh> 302 mod -today +anything
[task 302 mod -today +anything]
Modifying task 302 'Test Timewarrior'.
Modified 1 task.
tasksh> start 302
[task start 302]
Starting task a36684d6 'Test Timewarrior'.
Started 1 task.
Note: 'anything' is a new tag.
Tracking "Test Timewarrior" anything
Started 2021-09-24T08:14:21
Current 21
Total 0:00:00
You have more urgent tasks.
tasksh> stop 302
[task stop 302]
Stopping task a36684d6 'Test Timewarrior'.
Stopped 1 task.
Recorded "Test Timewarrior" anything
Started 2021-09-24T08:14:21
Ended 23
Total 0:00:02
```

Anything I can do to fix of help to solve the problem?

Thanks for your work!