Fix simplify guard clause in RSpec/ChangeByZero cop

Replace complex condition with a simpler guard clause

Author: rito.ishihara

lib/rubocop/cop/rspec/change_by_zero.rb

@@ -102,9 +102,7 @@ def on_send(node)
         private
 
         def register_offense(node, change_node)
-          if !node.parent.respond_to?(:send_type?) || !node.parent.send_type?
-            return
-          end
+          return unless node.parent.send_type?
 
           if compound_expectations?(node)
             add_offense(node,