Fix Apache segfault (#17)

Dockerfile

@@ -1,5 +1,5 @@
 # Alpine Linux with s6 service management
-FROM smebberson/alpine-base
+FROM smebberson/alpine-base:3.2.0
 
 	# Install Apache2 and other stuff needed to access svn via WebDav
 	# Install svn
@@ -7,7 +7,7 @@ FROM smebberson/alpine-base
 	# Create required folders
 	# Create the authentication file for http access
 	# Getting SVNADMIN interface
-RUN apk add --no-cache apache2 apache2-ctl apache2-utils apache2-webdav mod_dav_svn &&\
+RUN apk add --no-cache apache2 apache2-utils apache2-webdav mod_dav_svn &&\
 	apk add --no-cache subversion &&\
 	apk add --no-cache wget unzip php7 php7-apache2 php7-session php7-json php7-ldap &&\
 	apk add --no-cache php7-xml &&\	
@@ -23,6 +23,9 @@ RUN apk add --no-cache apache2 apache2-ctl apache2-utils apache2-webdav mod_dav_
 	ln -s /opt/svnadmin /var/www/localhost/htdocs/svnadmin &&\
 	chmod -R 777 /opt/svnadmin/data
 
+# Solve a sicurity issue (https://alpinelinux.org/posts/Docker-image-vulnerability-CVE-2019-5021.html)	
+RUN sed -i -e 's/^root::/root:!:/' /etc/shadow
+
 # Fixing https://github.com/mfreiholz/iF.SVNAdmin/issues/118
 ADD svnadmin/classes/util/global.func.php /opt/svnadmin/classes/util/global.func.php