chore(CI): update Python for Node 17

.travis.yml

@@ -13,6 +13,10 @@ before_install:
 install:
   - echo "Avoid Travis's npm auto-install"
 before_script: >
+  if [ -n "${UPDATE_PYTHON-}" ]; then
+    echo "Updating Python"
+    apk add --update --no-cache python3
+  fi
   npm install --legacy-peer-deps --no-save "eslint@${ESLINT}"
 notifications:
   email: false
@@ -29,6 +33,8 @@ jobs:
   include:
     - node_js: 'lts/*'
       env: LINT=true
+    - node_js: '17'
+      env: UPDATE_PYTHON=true
 after_success:
   - export NODE_ENV=production
   - npm run build