Corrects typo in error message displayed to user

Replaces "for a example" with the correct "for an example".
Merge pull request #2972 from gilles-leblanc/fix-typo

Corrects typo in error message displayed to the user
remove superfluous characters that cause error if entered verbatim
Merge pull request #2979 from chris-tsongas/ruby-version

remove superfluous characters that cause error if entered verbatim