Added PHP session extension

Author: TrafeX

Dockerfile

@@ -4,7 +4,7 @@ LABEL Maintainer="Tim de Pater <code@trafex.nl>" \
 
 # Install packages
 RUN apk --no-cache add php7 php7-fpm php7-mysqli php7-json php7-openssl php7-curl \
-    php7-zlib php7-xml php7-phar php7-intl php7-dom php7-xmlreader php7-ctype \
+    php7-zlib php7-xml php7-phar php7-intl php7-dom php7-xmlreader php7-ctype php7-session \
     php7-mbstring php7-gd nginx supervisor curl
 
 # Configure nginx