update docker localhost hostname

[jranson]

This patch changes references to docker.for.mac.localhost with the modern host.docker.internal to ensure demo and dev environments work on all platforms.

[coveralls]

Pull Request Test Coverage Report for Build 15783145500

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 4 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.02%) to 76.569%

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Files with Coverage Reduction	New Missed Lines	%
pkg/proxy/engines/cache.go	2	92.58%
pkg/proxy/engines/progressive_collapse_forwarder.go	2	96.52%

Totals
Change from base Build 15640374012:	-0.02%
Covered Lines:	15271
Relevant Lines:	19944

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💛 - Coveralls