Reference links broken in the manual

[Alexander Dax]

In the update where
005_protocol-specification.md
got split into
005_protocol-specification-rules.md
and
006_protocol-specification-processes.md
the references to each of the files seem to be not properly updated.

As an example, on the organisation section of https://tamarin-prover.github.io/manual/book/001_introduction.html
chapter 7 is still linked as https://tamarin-prover.github.io/manual/book/006_property-specification.html#sec:property_specification.
However, the new link should be
https://tamarin-prover.github.io/manual/book/007_property-specification.html#sec:property_specification.

[jdreier]

Should be fixed now.