Fix eco request content type

The go-rest dependency of the eco service was updated to use the more
correct application/json content type when posting JSON encoded data

https://github.com/ungerik/go-rest/commit/c3ee1de9e2197fe2812b818f25d2fc59fab9a13e
Merge pull request #1513 from jwalgran/topic/fix-eco-request-content-type

Fix eco request content type