spec_helper: retry failing CI tests.
spec_helper: retry failing CI tests.

This should help avoid a bit of the flakiness we see in builds at the
cost of a slight slowdown on retries.

vitorgalvao/brew,mahori/brew,mahori/brew,EricFromCanada/brew,nandub/brew,vitorgalvao/brew,JCount/brew,nandub/brew,claui/brew,claui/brew,konqui/brew,Homebrew/brew,JCount/brew,mahori/brew,sjackman/homebrew,claui/brew,claui/brew,konqui/brew,konqui/brew,reitermarkus/brew,sjackman/homebrew,JCount/brew,sjackman/homebrew,MikeMcQuaid/brew,reitermarkus/brew,Homebrew/brew,MikeMcQuaid/brew,EricFromCanada/brew,Homebrew/brew,vitorgalvao/brew,MikeMcQuaid/brew,nandub/brew,EricFromCanada/brew,konqui/brew,sjackman/homebrew,Homebrew/brew,JCount/brew,mahori/brew,EricFromCanada/brew,vitorgalvao/brew,nandub/brew,reitermarkus/brew,reitermarkus/brew,MikeMcQuaid/brew