add php7-mbstring

Author: etopian

Dockerfile

@@ -20,7 +20,7 @@ RUN echo 'http://dl-4.alpinelinux.org/alpine/edge/testing' >> /etc/apk/repositor
     php7-pdo_mysql php7-mysqli php7-session \
     php7-gd php7-iconv php7-mcrypt \
     php7-curl php7-opcache php7-ctype php7-apcu \
-    php7-intl php7-bcmath php7-dom php7-xmlreader mysql-client openssh-client git curl rsync && apk add -u musl
+    php7-intl php7-bcmath php7-mbstring php7-dom php7-xmlreader mysql-client openssh-client git curl rsync && apk add -u musl
 
 RUN rm -rf /var/cache/apk/*