Use verify_request_format! method to check valid request format

[fpenapita]

This commit fix a problem to be able to render error responses for
format distinct to html (for example json) because e.request.format is
returning a Mime::Type object that doesn’t match with the values in
self.class.respond_to that is a hash with keys :html, :json, etc

Using the responders’ verify_requested_format! we are getting exactly
the same goal delegating the tasks in the own responders gem.

[coveralls]

Pull Request Test Coverage Report for Build 1565

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-2.8%) to 59.016%

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Totals
Change from base Build 1563:	-2.8%
Covered Lines:	72
Relevant Lines:	122

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 1565

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-2.8%) to 59.016%

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Files with Coverage Reduction	New Missed Lines	%
lib/exception_handler/config.rb	1	77.78%

Totals
Change from base Build 1563:	-2.8%
Covered Lines:	72
Relevant Lines:	122

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💛 - Coveralls