awscli 1.3.23

- Updates awscli to the latest stable version (as of this writing).
- `brew uses awscli` returned no dependencies
- ran `brew install --verbose --debug awscli` and it installed without issue
- `brew test awscli` returned:
```bash
Testing awscli
==> /usr/local/Cellar/awscli/1.3.23/bin/aws --version
```
Which didn't seem very useful, but I'm not sure how to improve it. (Suggestions welcome).

Everything seems to be in order. Let me know if there is anything I can do to make this pull request more merge-able. 

Thanks for creating/maintaining homebrew!