update/release: fix missing variable definition

i forgot to include option.sh in this script,
during previous re-factoring. the cbfstoos variable
is now defined exclusively in option.sh, but other
scripts can set it to something else.

Signed-off-by: Leah Rowe <leah@libreboot.org>

script/update/project/release

@@ -6,6 +6,7 @@
 set -u -e
 
 . "include/err.sh"
+. "include/option.sh"
 
 eval "$(setvars "" vdir relname src_dirname srcdir _nogit _xm target romdir \
     microcode_required mode)"