Added stack download/install to travis script

.travis.yml

@@ -7,16 +7,12 @@ addons:
   apt:
     packages:
       - libsdl2-dev
-env:
-  - LD_LIBRARY_PATH=libsdl2
 before_install:
   # Download and install Haskell Stack
-  #- mkdir -p ~/.local/bin
-  #- export PATH=$HOME/.local/bin:$PATH
-  #- travis_retry curl -L https://www.stackage.org/stack/linux-x86_64 | tar xz --wildcards --strip-components=1 -C ~/.local/bin '*/stack'
-
-  # Download and build SDL
-  #- ./fetch.sh
+  - mkdir -p ~/.stack-home
+  - export PATH=$HOME/.stack-home:$PATH
+  - travis_retry wget https://www.stackage.org/stack/linux-x86_64 -O stack.tar
+  - tar xz -f stack.tar --wildcards --strip-components=1 -C ~/.stack-home '*/stack'
 install:
 #  - stack --no-terminal --install-ghc test --only-dependencies
    - true