chore: update CoreDNS to v1.7.0

[mboersma]

Reason for Change:
See https://coredns.io/2020/06/15/coredns-1.7.0-release/

Issue Fixed:

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[codecov]

Codecov Report

Merging #3608 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3608   +/-   ##
=======================================
  Coverage   73.14%   73.14%           
=======================================
  Files         147      147           
  Lines       25141    25141           
=======================================
  Hits        18389    18389           
  Misses       5620     5620           
  Partials     1132     1132           

Impacted Files	Coverage Δ
pkg/api/k8s_versions.go	99.20% <ø> (ø)

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[CecileRobertMichon]

/lgtm

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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