Update vfrcompile referenced uefi spec version from 2.3.1 to 2.4.

Signed-off-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2-buildtools/code/trunk/BaseTools@2628 c2973edb-eda0-4c78-bc6a-9341b269661f