Fix copypasta

Signed-off-by: Gilles Peskine <[email protected]>

Author: gilles-peskine-arm

docs/4.0-migration-guide.md

@@ -1,6 +1,6 @@
 # Migrating from Mbed TLS 3.x to TF-PSA-Crypto 1.0
 
-This guide details the steps required to migrate from Mbed TLS version 2.x to Mbed TLS version 3.0 or greater. Unlike normal releases, Mbed TLS 3.0 breaks compatibility with previous versions, so users, integrators and package maintainers might need to change their own code in order to make it work with Mbed TLS 3.0.
+This guide details the steps required to migrate from Mbed TLS version 3.x to Mbed TLS version 4.0 or greater. Unlike normal releases, Mbed TLS 4.0 breaks compatibility with previous versions, so users, integrators and package maintainers might need to change their own code in order to make it work with Mbed TLS 4.0.
 
 Here's the list of breaking changes; each entry should help you answer these two questions: (1) am I affected? (2) if yes, what's my migration path?