Don't use multiline strings for commands on Travis CI

Commands would otherwise fail silently.

.travis.yml

@@ -5,11 +5,11 @@ addons:
     packages:
     - luarocks
 
-before_install: |
-  pyenv global 3.6.3
-  pip3 install --user pre-commit
-  luarocks install --local luacheck
+install:
+  - pyenv global 3.6.3
+  - pip3 install --user pre-commit
+  - luarocks install --local luacheck
 
-script: |
-  "$HOME/.local/bin/pre-commit" run --all-files
-  "$HOME/.luarocks/bin/luacheck" .
+script:
+  - $HOME/.local/bin/pre-commit run --all-files
+  - $HOME/.luarocks/bin/luacheck .