Use the new coordinated_forks option coming in Test::Builder 1.5.0_7

See https://github.com/schwern/test-more/pull/367 and the issue/334 branch at
https://github.com/schwern/test-more/
Merge pull request #5 from schwern/fix_TB1.5

Use the new coordinated_forks option coming in Test::Builder 1.5.0_7