Update install script

- Change path to Homebrew as per brew.sh
- Remove unneccessary period in first print statement
- Change 'gcc' check from type_exists helper function to hardcoded
  function call as it appears to be failing on brand new test machine.
  Not sure why this breaks, but when testing `! type_exists 'gcc'` vs.
  `! $(type -P 'gcc')` I get different results.  I've also figured that
  with 'gcc' & 'git' commands you can call them immediately and if not
  present they'll invoke Install Command Line Developer Tools prompt.

Issue: #9