Improve defined? mutations

* Correct changelog reference

Changelog.md

@@ -2,7 +2,7 @@
 
 * Remove invalid mutation `foo or bar` to `!(foo or bar)` see #287
 * Add mutation from `#to_h` to `#to_hash` #218
-* Add mutation from `#defined?` to `true` / `false` #399
+* Add mutation from `#defined?` to `true` / `false` #334
 
 # v0.8.1 2015-07-24
 

lib/mutant/mutator/node/defined.rb

@@ -16,21 +16,10 @@ module Mutant
         #
         # @api private
         def dispatch
-          emit_expression_mutations do |node|
-            !n_self?(node)
-          end
-
-          emit_bools
-        end
-
-        # Emit booleans
-        #
-        # @return [undefined]
-        #
-        # @api private
-        def emit_bools
+          emit_singletons
           emit(N_TRUE)
-          emit(N_FALSE)
+
+          emit_expression_mutations { |node| !n_self?(node) }
         end
 
       end # Defined

meta/defined.rb

@@ -1,7 +1,7 @@
 Mutant::Meta::Example.add do
   source 'defined?(foo)'
 
+  singleton_mutations
   mutation 'defined?(nil)'
   mutation 'true'
-  mutation 'false'
 end