Add missing dependency to set.el

I had startup problems without the struct.el module being required since set.el
consumes `struct/update`.

configs/shared/.emacs.d/wpc/set.el

@@ -8,6 +8,7 @@
 
 (require 'ht) ;; friendlier API for hash-tables
 (require 'dotted)
+(require 'struct)
 
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 ;; Wish List