arm-bsp/docs: Set required Kas version to 3.0 for fvp-baser-aemv8r64

poky master has changed a variable name to BB_ENV_PASSTHROUGH_ADDITIONS.
Support for this has been added in Kas 3.0

Issue-Id: SCM-3881
Signed-off-by: Peter Hoyes <Peter.Hoyes@arm.com>
Change-Id: Ib42f79d144422272b2dd17fe0515da96909219eb
Signed-off-by: Jon Mason <jon.mason@arm.com>

meta-arm-bsp/documentation/fvp-baser-aemv8r64.md

@@ -98,7 +98,7 @@ Install the required packages for the build host:
 https://docs.yoctoproject.org/singleindex.html#required-packages-for-the-build-host
 
 Kas is a setup tool for bitbake based projects. The minimal supported version
-is 2.6, install it like so:
+is 3.0, install it like so:
 
     pip3 install --user kas