Fix link to Debian install instructions
The link for the Debian install instructions was mistakenly pointing to
the RPM instructions. This commit fixes the reference.
Relates
[[deb]]
=== Install Elasticsearch with Debian Package
-The Debian package for Elasticsearch can be <<install-rpm,downloaded from our website>>
+The Debian package for Elasticsearch can be <<install-deb,downloaded from our website>>
or from our <<deb-repo,APT repository>>. It can be used to install
Elasticsearch on any Debian-based system such as Debian and Ubuntu.
