update travis

Author: nobrakal

.travis.yml

@@ -45,12 +45,11 @@ install:
 script:
 # Build the package, its tests, and its docs and run the tests
 - stack --no-terminal bench --no-run-benchmarks
-- PREFIX=.stack-work/dist/x86_64-linux/Cabal-2.2.0.1/build
+- PREFIX=.stack-work/dist/x86_64-linux/Cabal-2.4.0.1/build
 - if [ $DO = SPACE ]; then travis_wait 30 $PREFIX/space/space; else $PREFIX/time/time run --part $STEP --of 4  -g '("Mesh",2)' -g '("Clique",2)' ; fi;
 
 before_install:
 # Download and unpack the stack executable
 - mkdir -p ~/.local/bin
 - export PATH=$HOME/.local/bin:$PATH
 - travis_retry curl -L https://get.haskellstack.org/stable/linux-x86_64.tar.gz | tar xz --wildcards --strip-components=1 -C ~/.local/bin '*/stack'
-