chore: use yarn on Travis/macOS

.travis.yml

@@ -9,14 +9,12 @@ node_js:
 - '8'
 - '10'
 cache:
-- apt: true
 - directories:
-  - "node_modules"
   - "$HOME/.electron"
+- npm: true
+- yarn: true
 before_install: test/ci/before_install.sh
-install:
-- npm install
-- npm update
+install: if [[ "$TRAVIS_OS_NAME" = "osx" ]]; then yarn; else npm install && npm update; fi
 before_script: test/ci/_before_script.js
 after_success: npm run codecov
 branches:
@@ -25,6 +23,7 @@ branches:
   - /^v\d+\.\d+\.\d+/
 env:
   global:
+    - YARN_GPG=no
     # prevent wine popup dialogs about installing additional packages
     - WINEDLLOVERRIDES="mscoree,mshtml="
     - WINEDEBUG="-all"

test/ci/before_install.sh

@@ -9,8 +9,11 @@ case "$TRAVIS_OS_NAME" in
     ;;
   "osx")
     "$(dirname $0)"/codesign/import-testing-cert-ci.sh
-    npm install wine-darwin@1.9.17-1
+    npm install --no-save wine-darwin@1.9.17-1
     # Setup ~/.wine by running a command
     ./node_modules/.bin/wine hostname
+    if [[ -n "$TRAVIS" ]]; then
+        npm install -g yarn
+    fi
     ;;
 esac