install Bash autocompletion on maxosx

macosx_install_autocompletion

# check default bash version installed 
$ echo $BASH_VERSION
3.2.57(1)-release

# install a new version of bash since  autocompletion is supported from version 4.1.x
$ brew install bash

# make sure the new bash verison is added on /etc/shells 
echo '/usr/local/bin/bash' | sudo tee -a /etc/shells

# change default shell being used
$ chsh -s /usr/local/bin/bash

# confirm the change of the default shell
$ echo $BASH_VERSION
4.4.12(1)-release

# install Bash autocompletion with brew 
$ brew install bash-completion
$ brew tap homebrew/completions