[Minor] Debian: add missing sodium dependency

Required since rspamd 2.0. Even Debian Jessie ships 1.0.0, so add it
unconditionally.

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, 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, libicu-dev, zlib1g-dev, libunwind-dev | libunwind8-dev, libhyperscan-dev [amd64 i386]
+Build-Depends: debhelper (>= 9), dpkg-dev (>= 1.16.1~), cmake, 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, libicu-dev, zlib1g-dev, libunwind-dev | libunwind8-dev, libhyperscan-dev [amd64 i386], libsodium-dev
 Standards-Version: 3.9.6
 Homepage: https://rspamd.com
 Vcs-Git: git://github.com/vstakhov/rspamd.git