Fix home brew updating failure

Problem Description

After a few weeks sorting up and working with Python3 on my Mac Book Pro, the brew update failed to update and reported an error of aws command not found.

> brew update
aws codecommit credential-helper $@ get: aws: command not found
fatal: could not read Username for '': terminal prompts disabled

^Cerror: did not send all necessary objects


The solution is straight through. Since aws cli is not found, it is a missed step in migrating Mac development environment from Python2 to Python3 -- the corresponding aws cli is not installed well to Python3.

My python environment is managed via PyEnv. When a new python version is installed, the upstream depeendencies are not maintained via requirement.txt so it needs a manual step to re-enable awscli.  

>pip3 install awscli --upgrade