user_guide: Update tool version requirements

Merged Darryl Green requested to merge github/fork/CJKay/user-guide into master

Created by: CJKay

The tools used to test the firmware internally have been updated, and so the documentation has been updated to reflect the new version requirements.

Change-Id: If5c9e9a9cfd614be6521d25bb0cb55b4e585615c Signed-off-by: Chris Kay chris.kay@arm.com

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