Fix a setup error of TreeFrog framework

[treefrogframework]

Fix a setup error of treefrog framework.

I could not reproduce the following setup error on my environment, but maybe fixed.
http://tfb-logs.techempower.com/round-15/preview-2/treefrog/out.txt

[mention-bot]

Thanks @treefrogframework for contributing to The Framework Benchmarks! @msmith-techempower, @nbrady-techempower and @aoym, code you've worked on has been modified. If you have the chance, please review. If you wish to unsubscribe from these notices, please open a Pull Request with the commit message [ci skip] and your github name added to the userBlacklist array in the .mention-bot file.

[mention-bot]

Thanks @treefrogframework for contributing to The Framework Benchmarks! @msmith-techempower, @nbrady-techempower and @aoym, code you've worked on has been modified. If you have the chance, please review. If you wish to unsubscribe from these notices, please open a Pull Request with the commit message [ci skip] and your github name added to the userBlacklist array in the .mention-bot file.