Fixing possible range for week_of_month type

[tayjohno]

Summary of changes

Pretty straightforward change to make the type specification match the actual possible outputs from the existing function. See #703 for full details, but in summary the week_of_month function can return values up to 6, but the type currently specifies that it should return a value between 1 and 5.

iex> Timex.week_of_month(2022,1,31)
6

January 2022 Calendar:

week  Su Mo Tu We Th Fr Sa

1                       01
2     02 03 04 05 06 07 08
3     09 10 11 12 13 14 15
4     16 17 18 19 20 21 22
5     23 24 25 26 27 28 29
6     30 31

I searched through the application, and this function (Timex.week_of_month) was the only place where this type is being used.

Checklist

• [NA] New functions have typespecs, changed functions were updated
• [NA] Same for documentation, including moduledocs
• [NA] Tests were added or updated to cover changes
• Commits were squashed into a single coherent commit
• Notes added to CHANGELOG file which describe changes at a high-level