chore(docker): update service name to more general php

Author: koshuang

docker-compose.yml

@@ -1,7 +1,7 @@
 version: '3.4'
 
 services:
-  php7:
-    image: thecodingmachine/php:7.3-v3-slim-apache
+  php:
+    image: thecodingmachine/php:7.4-v4-slim-apache
     volumes:
       - ./:/var/www/html