Updated DockerFile for php

Removed mysql duplicate installation

Author: hiteshacc24

php/Dockerfile

@@ -5,8 +5,6 @@ RUN apk update; \
     apk upgrade;
 
 # Install MySql
-RUN docker-php-ext-install mysqli
-
 RUN docker-php-ext-install mysqli pdo pdo_mysql
 
 # Install Composer
@@ -81,4 +79,4 @@ RUN apk add --update \
         php7-bcmath \
         php7-memcached \
         php7-oauth \
-        php7-apcu
+        php7-apcu