rbenv global version of ruby vs Sierra ruby version
I entered this:

echo 'if which rbenv &gt; /dev/null; then eval "$(rbenv init -)"; fi' &gt;&gt; ~/.bash_profile source ~/.bash_profile


but it should be:

echo 'if which rbenv &gt; /dev/null; then eval "$(rbenv init -)"; fi' &gt;&gt; ~/.bash_profile
source ~/.bash_profile


...now it works fine.