Allow spaces after the . operator if followed by a comment.

Summary: Currently, 'foo'. // Some comment is not allowed by the ArcanistXHPASTLinter::LINT_BINARY_EXPRESSION_SPACING rule. I believe that in the case of a trailing comment, we should allow whitespace after the . operator.

Test Plan: Wrote and executed a unit test for this case.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9438