Debian: Add missing build dependencies.

debian/control

@@ -2,7 +2,7 @@ Source: rspamd
 Section: mail
 Priority: extra
 Maintainer: Mikhail Gusarov <dottedmag@debian.org>
-Build-Depends: debhelper (>= 9), dpkg-dev (>= 1.16.1~), cmake, libevent-dev (>= 1.3), libglib2.0-dev (>= 2.16.0), libluajit-5.1-dev [amd64 armel armhf i386 kfreebsd-i386 mips mipsel powerpc powerpcspe] | liblua5.1-dev, libpcre3-dev, libssl-dev (>= 1.0), libcurl4-openssl-dev, libsqlite3-dev, libmagic-dev, perl, dh-systemd, libjemalloc-dev, ragel
+Build-Depends: debhelper (>= 9), dpkg-dev (>= 1.16.1~), cmake, libevent-dev (>= 1.3), libglib2.0-dev (>= 2.16.0), libluajit-5.1-dev [amd64 armel armhf i386 kfreebsd-i386 mips mipsel powerpc powerpcspe] | liblua5.1-dev, libpcre3-dev, libssl-dev (>= 1.0), libcurl4-openssl-dev, libsqlite3-dev, libmagic-dev, perl, dh-systemd, libjemalloc-dev, ragel, libfann-dev (>= 2.2.0), libgd-dev (>= 2.2.4), libicu-dev
 Standards-Version: 3.9.6
 Homepage: https://rspamd.com
 Vcs-Git: git://github.com/vstakhov/rspamd.git