Update packages and add perl-xml-sig

Dockerfile

@@ -45,7 +45,7 @@ RUN sed -n 's/main/testing/p' /etc/apk/repositories >> /etc/apk/repositories &&
         perl-xml-tidy perl-xml-writer perl-xml-xpath perl-yaml perl-yaml-tiny \
         perl-file-mmagic perl-net-saml2 imagemagick-perlmagick graphviz \
         odt2txt antiword lynx poppler-utils perl-email-address-xs \
-        perl-crypt-openssl-verify iwatch  --update-cache && \
+        perl-crypt-openssl-verify perl-xml-sig iwatch  --update-cache && \
         # perl-libapreq2 -- Apache2::Request - Here for completeness but we use nginx \
         rm -fr /var/cache/apk/APKINDEX.*