upgrade to latest packages and gitlab API

latests rocket_codegen, diesel and hyper. doesn't share a rustc version that works for all of them

• rocket_codegen: rustc >= nightly-2018-05-30
• https://github.com/SergioBenitez/Rocket/issues/660 rustc < 2018-06-09
• https://github.com/diesel-rs/diesel/issues/1700 rustc < nightly-2018-05-14

closes !27 (closed)