Fix 'chsh' by checking '/etc/shells' instead of using 'which'
Fix 'chsh' by checking '/etc/shells' instead of using 'which'

fix test for chsh in install
in case $SHELL is zsh but not the last one in /etc/shells
fixes #3026 fixes #3779 fixes #3780

erwinvaneijk/oh-my-zsh,erwinvaneijk/oh-my-zsh