fix performance problem introduced by css-variable transformer

Atlassian Update – 16 November 2017 Hi everyone, The issue has not collected enough votes, watches, comments or support cases during it's lifetime. In this sense overal interest in the reported problem is low. Jira team is focusing on bigger and more impactful issues at the moment and we are not likely to look at the current bug soon. Therefore I'm resolving the issue as Timed Out . Atlassian will continue to watch issue for the further updates, so please don't hesitate to share your feedback in the issue comments. Cheers, Ignat Alexeyenko Jira bugmaster.