bugfix: path-based header injection

[jranson]

PR for #671

[coveralls]

Pull Request Test Coverage Report for Build 15475705570

Details

• 3 of 22 (13.64%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall first build on jr/path-configs-fix at 76.5%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/proxy/engines/httpproxy.go	2	3	66.67%
pkg/proxy/headers/headers.go	1	19	5.26%

Totals
Change from base Build 15391613504:	76.5%
Covered Lines:	15271
Relevant Lines:	19962

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💛 - Coveralls