Include local aliases file

* `.aliases.local` should be used to add personal aliases
Source ~/.zshrc.local if it exists

Follows the pattern of:

* ~/.aliases.local in ce7ad49
* ~/.gitconfig.local in 8e141fe
* ~/.vimrc.local in a666267

Use consistent:

* `source`ing style.
* commenting style.

I am using ~/.zshrc.local as a home for `eval "$(rbenv init -)"`.
Remove "DO NOT EDIT BELOW THIS LINE" convention

It has been superceded by a `.local` suffix convention.
Git push to current, not upstream

The primary use case for me is to `git push staging` and `git push
production` from the master branch using our typical git workflow:

https://github.com/thoughtbot/guides/tree/master/protocol#deploy
Make the migrate alias faster

This was loading up the environment four times when it really only needs
to happen twice.