Disable the "oldtime" feature of chrono

[Rustin170506]

This feature, enabled by default in chrono versions <5, includes a dependency on the deprecated [email protected]. A security advisory is issued for this verion of time.

Some details available here: chronotope/chrono#602

[Rustin170506]

➜  rustup git:(master) cargo tree -p time          
time v0.3.20
├── itoa v1.0.6
├── time-core v0.1.0
└── time-macros v0.2.8 (proc-macro)
    └── time-core v0.1.0

➜  rustup git:(master) cargo tree -p time -i
time v0.3.20
└── git-testament-derive v0.1.14 (proc-macro)
    └── git-testament v0.2.4
        └── rustup v1.26.0 (/Users/hi-rustin/vsc/rustup)