Update libfreetype package name

Author: J0WI

php/content.md

@@ -54,7 +54,7 @@ For example, if you want to have a PHP-FPM image with the `gd` extension, you ca
 ```dockerfile
 FROM %%IMAGE%%:7.4-fpm
 RUN apt-get update && apt-get install -y \
-		libfreetype6-dev \
+		libfreetype-dev \
 		libjpeg62-turbo-dev \
 		libpng-dev \
 	&& docker-php-ext-configure gd --with-freetype --with-jpeg \