Make semicolon optional in do-while in >=ES6
Revert "Merge branch 'do-optional-semicolon' of https://github.com/sebmck/acorn"

This reverts commit c526814896711439b89f613fe0412aad4c1730a8, reversing
changes made to e7fea263dac65061941a4cee25c7a84c4e50c8bf.
Merge branch 'do-optional-semicolon' of https://github.com/sebmck/acorn