Try fixing travis build

.travis.yml

@@ -1,42 +1,34 @@
-# This file has been generated -- see https://github.com/hvr/multi-ghc-travis
-language: c
 sudo: false
+language: minimal
+git:
+  submodules: false  # whether to recursively clone submodules
 
 cache:
   directories:
-    - $HOME/.cabsnap
-    - $HOME/.cabal/packages
+    - $HOME/.stack
 
 before_cache:
   - rm -fv $HOME/.cabal/packages/hackage.haskell.org/build-reports.log
   - rm -fv $HOME/.cabal/packages/hackage.haskell.org/00-index.tar
 
-matrix:
-  include:
-    - env: CABALVER=1.24 GHCVER=8.2.2
-      compiler: ": #GHC 8.2.2"
-      addons: {apt: {packages: [cabal-install-1.24,ghc-8.2.2], sources: [hvr-ghc]}}
-
 before_install:
- - unset CC
- - mkdir -p ~/.local/bin
- - export PATH=$HOME/.local/bin:/opt/ghc/$GHCVER/bin:/opt/cabal/$CABALVER/bin:$PATH
- - travis_retry curl -L https://www.stackage.org/stack/linux-x86_64 | tar xz --wildcards --strip-components=1 -C ~/.local/bin '*/stack'
+  # This is an unfortunate hack that changes ssh paths into http path, so that
+  # we can do a read-only clone of our submodules without worrying about ssh
+  # keys.
+  - sed -i 's/git@github.com:/https:\/\/github.com\//' .gitmodules
+  - git submodule update --init
+
+  # Download and unpack the stack executable
+  - mkdir -p $HOME/.local/bin
+  - export PATH=$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'
+
 
 install:
- - cabal --version
- - echo "$(ghc --version) [$(ghc --print-project-git-commit-id 2> /dev/null || echo '?')]"
- - if [ -f $HOME/.cabal/packages/hackage.haskell.org/00-index.tar.gz ];
-   then
-     zcat $HOME/.cabal/packages/hackage.haskell.org/00-index.tar.gz >
-          $HOME/.cabal/packages/hackage.haskell.org/00-index.tar;
-   fi
- - travis_retry cabal update -v
- - sed -i 's/^jobs:/-- jobs:/' ${HOME}/.cabal/config
+ - travis_wait stack --no-terminal --skip-ghc-check setup
 
 # Here starts the actual work to be performed for the package under test;
 # any command which exits with a non-zero exit code causes the build to fail.
 script:
- - travis_wait stack --no-terminal --skip-ghc-check setup
  - stack --stack-yaml stack.ghc-8.6.3.yaml build macaw-x86 macaw-x86-symbolic
  - stack --stack-yaml stack.ghc-8.6.3.yaml test macaw-x86