Add set_deref_options call to Promise constructor

Fixes unintitialised variable warnings, and matches delay.rb

Author: rkday

lib/concurrent/promise.rb

@@ -204,6 +204,7 @@ def initialize(opts = {}, &block)
       @children = []
 
       init_obligation
+      set_deref_options(opts)
     end
 
     # @return [Promise]