Setup Imagick for Travis

To avoid error from phpstan about class not found

.travis.yml

@@ -54,6 +54,10 @@ before_script:
     - echo "memory_limit=-1" >> ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/travis.ini
     - phpenv config-rm xdebug.ini || echo "xdebug not available"
     - composer self-update --no-progress
+    # install imagick
+    - pear config-set preferred_state beta
+    - pecl channel-update pecl.php.net
+    - yes | pecl install imagick
 
 script:
     - travis_wait bash composer install -o --no-interaction --no-progress --prefer-dist