fix format of composer.json

Author: miya0001

composer.json

@@ -21,6 +21,6 @@
     "require-dev": {
         "behat/behat": "~2.5",
         "wp-cli/wp-cli": "*",
-        "phpunit/phpunit": "~5.6",
+        "phpunit/phpunit": "~5.6"
     }
 }