covr 3.3.1

• Fix inadvertent regression in return visibility when functions are covered.
  covr versions prior to 3.3.0 surrounded each statement in { blocks. covr
  3.3.0 switched to using ({, but this caused an inadvertent regression, as
  ( will make the result visible it is the last expression in a function.
  Using if (TRUE) { restores the previous behavior. (#391, #392)