fix(travis): Change where `stack docker pull` happens

.travis.yml

@@ -7,7 +7,6 @@ addons:
     packages:
     - libgmp-dev
 before_install: bash contrib/travis/before-install.sh
-before_script: stack docker pull
 script: stack test --no-terminal --install-ghc --copy-bins
 cache:
   directories:

contrib/travis/before-install.sh

@@ -9,7 +9,7 @@ export PATH=$HOME/.local/bin:$PATH
 curl -L https://www.stackage.org/stack/linux-x86_64 \
   | tar xz --wildcards --strip-components=1 -C ~/.local/bin '*/stack'
 
-stack setup
+stack docker pull
 stack install hscolour
 
 docker login -e="." -u="$DOCKER_USERNAME" -p="$DOCKER_PASSWORD" quay.io