The Bool field of Terminated is new, as is the documentation:

data ProcessStatus
   = Exited ExitCode        -- ^ the process exited by calling
                            -- @exit()@ or returning from @main@
   | Terminated Signal Bool -- ^ the process was terminated by a
                            -- signal, the @Bool@ is @True@ if a core
                            -- dump was produced
   | Stopped Signal         -- ^ the process was stopped by a signal
   deriving (Eq, Ord, Show)

This is an API change, hence will need a major version bump.