Update bash-it sha to latest

Includes

* chruby(-auto) plugin rename [306f7b1587](https://github.com/revans/bash-it/commit/306f7b1587486cd4ed20726f64ecc2bf96334d47)
* system-ruby display in prompt [5ef3f817fe](https://github.com/revans/bash-it/commit/5ef3f817fef1aff10f34881f856a60f4066ac1ea)