Add PHP 7.3 image

Signed-off-by: Riddhesh Sanghvi <[email protected]>

Author: mrrobot47

img-versions.json

@@ -6,6 +6,7 @@
     "easyengine/nginx": "v4.0.0",
     "easyengine/php": "v4.0.2",
     "easyengine/php5.6": "v4.0.0",
+    "easyengine/php7.3": "v4.0.0",
     "easyengine/postfix": "v4.0.0",
     "easyengine/redis": "v4.0.0",
     "easyengine/newrelic-daemon": "v4.0.0"