Remov omitempty on domain records name

[ddymko]

Description

If you try to create a DNS record that doesn't have a name the omitempty we currently have won't get passed to the API which causes issues.

Related Issues

vultr/terraform-provider-vultr#105

Checklist:

• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you linted your code locally prior to submission?
• Have you successfully ran tests with your changes locally?

[codecov]

Codecov Report

Merging #120 (fe19cd6) into master (8c2f970) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #120   +/-   ##
=======================================
  Coverage   49.14%   49.14%           
=======================================
  Files          23       23           
  Lines        1168     1168           
=======================================
  Hits          574      574           
  Misses        348      348           
  Partials      246      246           

Impacted Files	Coverage Δ
domain_records.go	45.45% <ø> (ø)

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