Preserve order of object properties

[yamafaktory]

• By default, serde_json is not preserving the entries in the order they are inserted into the map https://github.com/serde-rs/json/blob/master/src/value/mod.rs#L196-L200. Use the preserve_order feature flag to enable that option.
• Fix the after_success benchmark comparison step failure by increasing the git depth Travis occasionaly fails trying to checkout revision using valid commit hash travis-ci/travis-ci#6690.