Dockerfile: add php-yaml

Dockerfile

@@ -6,7 +6,7 @@ RUN curl -sSLf -o /usr/local/bin/install-php-extensions https://github.com/mloca
     apt update &&\
     apt install -y clamav clamdscan clamav-daemon gdal-bin &&\
     sed -i -e 's/^User .*/User root/g' /etc/clamav/clamd.conf &&\
-    install-php-extensions @composer fileinfo iconv intl mbstring simplexml zip zlib bz2 phar
+    install-php-extensions @composer fileinfo iconv intl mbstring simplexml zip zlib bz2 phar yaml
 RUN freshclam --foreground
 COPY . /opt/filechecker
 RUN cd /opt/filechecker &&\