Fixed the utf8_decode error

Dockerfile

@@ -12,13 +12,19 @@ MAINTAINER Miroslav Prasil <miroslav@prasil.info>
 ARG DOKUWIKI_VERSION=2017-02-19e
 ARG DOKUWIKI_CSUM=09bf175f28d6e7ff2c2e3be60be8c65f
 
-ENV LAST_REFRESHED 25. October 2017
-
 # Update & install packages & cleanup afterwards
 RUN DEBIAN_FRONTEND=noninteractive \
     apt-get update && \
     apt-get -y upgrade && \
-    apt-get -y install wget lighttpd php-cgi php-gd php-ldap php-curl php-mbstring && \
+    apt-get -y install \
+        wget \
+        lighttpd \
+        php-cgi \
+        php-gd \
+        php-ldap \
+        php-curl \
+        php-xml \
+        php-mbstring && \
     apt-get clean autoclean && \
     apt-get autoremove && \
     rm -rf /var/lib/{apt,dpkg,cache,log}