Update all pages which talk about the Java version, for instance https://documentation.magnolia-cms.com/display/DOCS/Certified+stack (but there is a bunch of others).
The 5.4.x branch still can be run on 1.7!

Procedure:

• Do it only on the DOCS55 and the NOW space.
• This said, let's check every page we move / copy from DOCS to DOCS55
• Do not change it neither on DOCS (which becomes DOCS54) nor on DOCS53
• At the end search and replace for those which we have forgotten