chore: update gitignore

Includes gatsbyjs#246 and adds tests/_output

.gitignore

@@ -1,5 +1,4 @@
 .DS_Store
-node_modules
 phpcs.xml
 phpunit.xml
 Thumbs.db
@@ -14,23 +13,18 @@ node_modules/
 .idea
 .vscode
 .github_changelog_generator
-!vendor/
-vendor/*
+vendor/
 !vendor/autoload.php
-!vendor/composer
-!vendor/firebase
-!vendor/ircmaxell
-vendor/composer/installed.json
-vendor/composer/*/
-!vendor/composer/semver/*
-!tests
+!vendor/composer/
+!vendor/firebase/
+!vendor/ircmaxell/
 tests/*.suite.yml
+tests/_output/
 build/
-coverage/*
+coverage/
 schema.graphql
 phpunit.xml
 docker-output
-composer.lock
 c3.php
 .log/
 php-coveralls.phar