Fix null value in DigitalOcean create a record

[karantan]

Fix null value in DigitalOcean create a record

Description

This fixes "field could not be unmarshalled" error when trying to send
'null' as a boolean value. It needs to be int or bool, not a string.

Ref: https://developers.digitalocean.com/documentation/v2/#create-a-new-domain-record

Status

Replace this: describe the PR status. Examples:

• done, ready for review

Checklist (tick everything that applies)

• Code linting (required, can be done after the PR checks)
• Documentation
• Tests
• [ ] ICLA (required for bigger changes)

[Kami]

LGTM 👍

I wonder if null string is a left over from previous version of their API or similar.

[Kami]

I see update_record() does the same thing so I will update that code as well.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.01%. Comparing base (cc5987b) to head (7b88819).
⚠️ Report is 1778 commits behind head on trunk.

Additional details and impacted files

@@           Coverage Diff           @@
##            trunk    #1570   +/-   ##
=======================================
  Coverage   83.01%   83.01%           
=======================================
  Files         394      394           
  Lines       84990    84990           
  Branches     9038     9038           
=======================================
  Hits        70550    70550           
  Misses      11373    11373           
  Partials     3067     3067           

Files with missing lines	Coverage Δ
libcloud/dns/drivers/digitalocean.py	92.59% <100.00%> (ø)

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