build app image with php7-iconv

src/app/Dockerfile

@@ -4,7 +4,7 @@ EXPOSE 9000/tcp
 RUN apk add --no-cache dcron php7 php7-fpm \
 	php7-pdo php7-gd php7-pgsql php7-pdo_pgsql php7-mbstring \
 	php7-intl php7-xml php7-curl php7-session \
-	php7-dom php7-fileinfo php7-json \
+	php7-dom php7-fileinfo php7-json php7-iconv \
 	php7-pcntl php7-posix php7-zip php7-openssl \
 	git postgresql-client sudo rsync