Update deprecated syntax

Author: johnroyer

dev/docker/Dockerfile

@@ -25,5 +25,5 @@ COPY --from=composer:latest /usr/bin/composer /bin/composer
 RUN mv "$PHP_INI_DIR/php.ini-production" "$PHP_INI_DIR/php.ini" && \
     sed -i 's/memory_limit = 128M/memory_limit = 512M/g' "$PHP_INI_DIR/php.ini"
 
-ENV APACHE_DOCUMENT_ROOT /app/public
+ENV APACHE_DOCUMENT_ROOT="/app/public"
 WORKDIR /app