Fix build by not running test cases

[jaccokrijnen]

Fix the build by changing build-type to Simple, meaning that the tests are not run anymore. The tests were written with an old version (<2.0) of QuickCheck (which requires base <4) and could therefore not compile.

[jaccokrijnen]

So it turns out that since cabal-1.24, you have to define a custom-build stanza in the .cabal file (which is not completely obvious: haskell/cabal#5278). Adding such a stanza also fixes it, but gives the following warning:

/home/jacco/projects/permutation/dist-newstyle/build/x86_64-linux/ghc-8.4.1/permutation-0.5.0.5/setup/setup.hs:14:11: warning: [-Wdeprecations]
    In the use of ‘runTests’
    (imported from Distribution.Simple, but defined in Distribution.Simple.UserHooks):
    Deprecated: "Please use the new testing interface instead!"
   |
14 |          {runTests=testing}
   |           ^^^^^^^^

And indeed, using the most recent cabal, the runTests hook is ignored (and even if it wasn't, it would probably fail similarly to the quickcheck error from https://travis-ci.org/spacekitteh/permutation/jobs/47721007)