Added TravixCI, eslint, phpcs.

.gitignore

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+node_modules/

.travis.yml

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+language: php
+
+notifications:
+  email:
+    on_success: never
+    on_failure: change
+
+php:
+  - 5.6
+
+env:
+  - WP_VERSION=latest WP_MULTISITE=0
+
+before_script:
+  - yarn install
+  - bash bin/install-wp-tests.sh wordpress_test root '' localhost $WP_VERSION
+
+script:
+  - find . -name composer -prune -o -name node_modules -prune -o -name '*.php' -exec php -lf {} \; >/dev/null
+  - yarn run php-codesniffer
+  - yarn run js-lint
+
+deploy:
+  - provider: script
+    script: chmod +x ./node_modules/@boldgrid/wordpress-tag-sync/release.sh && ./node_modules/@boldgrid/wordpress-tag-sync/release.sh
+    skip_cleanup: true
+    on:
+      tags: true
+  - provider: releases
+    api_key: "${GITHUB_TOKEN}"
+    file: "shrinkwrap_images.zip"
+    skip_cleanup: true
+    on:
+      tags: true

package.json

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+{
+ "scripts": {
+  "js-lint": "prettier-eslint **/*.js --list-different",
+  "js-lint-fix": "prettier-eslint **/*.js --write",
+  "install-codesniffs": "php node_modules/PHP_CodeSniffer/bin/phpcs --config-set installed_paths node_modules/WordPress-Coding-Standards/",
+  "php-codesniffer": "npm run install-codesniffs && node_modules/PHP_CodeSniffer/bin/phpcs -p -s --report=emacs --report-width=220 --standard=WordPress-Docs --standard=WordPress-Extra --ignore=*/node_modules/* --extensions=php --exclude=WordPress.Files.FileName ."
+ },
+ "devDependencies": {
+  "@boldgrid/wordpress-tag-sync": "^1.3.0",
+  "PHP_CodeSniffer": "https://github.com/squizlabs/PHP_CodeSniffer/",
+  "WordPress-Coding-Standards": "https://github.com/WordPress-Coding-Standards/WordPress-Coding-Standards.git#master",
+  "eslint": "^4.19.1",
+  "eslint-config-wordpress": "^2.0.0",
+  "eslint-plugin-html": "^4.0.2",
+  "prettier-eslint": "^8.8.1",
+  "prettier-eslint-cli": "^4.7.1"
+ }
+}