Correct capitalization for the Content-Type header
minor #4345 Correct capitalization for the Content-Type header (GeertDD)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #4345).

Discussion
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Correct capitalization for the Content-Type header

http://tools.ietf.org/html/rfc7231#section-3.1.1.5

Commits
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74dc6f8 Correct capitalization for the Content-Type header