Auto merge of #1917 - jtgeibel:update/num, r=carols10cents

Update chrono, dotenv, num-*, migrations_macros, and derive_deref

Overall, this drops 16 old versions of dependencies.  The `num-*` crates are on the list at #1805, but overall I think this is low risk to deploy together.

* `cargo update -p num -p num-iter -p num-traits --aggressive`
* `cargo update -p chrono`
* `cargo update -p migrations_macros -p derive_deref`
* Update to latest `dotenv`

Author: bors