travis: Move the 8.4.1 builders to 8.4.2.
This ought to fix the build matrix. I believe the issue is GHC trac 5129, where evaluate is being miscompiled: in cabal-testsuite's Test.Cabal.Server, in the function readUntilEnd, the 'read' function is protected by an 'if' to ensure that it doesn't result in the dreaded 'no parse'. However, some sophisticated putStrLn debugging has revealed that it is being called in *both* branches, not just the safe one; this is the worst sort of heisenbug because it vanished when I put a putStrLn before the evaluate! Since the evaluate function is fixed in 8.4.2 and bumping to 8.4.2 has a patch for trac 5129, this is as fixed as it can get.
Showing with 4 additions and 4 deletions