Docker missing PHP extensions

php7-iconv php7-xmlreader php7-zlib
https://github.com/FreshRSS/FreshRSS/issues/1821

Docker/Dockerfile

@@ -3,7 +3,7 @@ FROM alpine:3.7
 RUN apk add --no-cache \
 	apache2 php7-apache2 \
 	php7 php7-curl php7-gmp php7-intl php7-mbstring php7-xml php7-zip \
-	php7-ctype php7-dom php7-fileinfo php7-json php7-session php7-simplexml \
+	php7-ctype php7-dom php7-fileinfo php7-iconv php7-json php7-session php7-simplexml php7-xmlreader php7-zlib \
 	php7-pdo_sqlite \
 	php7-pdo_mysql \
 	php7-pdo_pgsql