Add mutation Hash#[] -> Hash#key?

Fixes #456

Changelog.md

@@ -1,3 +1,7 @@
+# Master (unreleased)
+
+* Add mutation from `Hash#[]` to `Hash#key?` (#511)
+
 # v0.8.8 2015-xx-xx
 
 * Drop support for rspec-3.2

lib/mutant/mutator/node/send.rb

@@ -27,7 +27,7 @@ module Mutant
           to_a:          %i[to_ary],
           to_h:          %i[to_hash],
           at:            %i[fetch],
-          :[] =>         %i[at fetch],
+          :[] =>         %i[at fetch key?],
           :== =>         %i[eql? equal?],
           :>= =>         %i[> == eql? equal?],
           :<= =>         %i[< == eql? equal?],

meta/send.rb

@@ -405,6 +405,7 @@ Mutant::Meta::Example.add do
   mutation 'foo[]'
   mutation 'foo.at(1)'
   mutation 'foo.fetch(1)'
+  mutation 'foo.key?(1)'
   mutation 'self[1]'
   mutation 'foo[0]'
   mutation 'foo[2]'
@@ -420,6 +421,7 @@ Mutant::Meta::Example.add do
   mutation 'self.foo'
   mutation 'self.foo.at()'
   mutation 'self.foo.fetch()'
+  mutation 'self.foo.key?()'
   mutation 'self[]'
   mutation 'foo[]'
 end
@@ -433,6 +435,7 @@ Mutant::Meta::Example.add do
   mutation 'self[]'
   mutation 'self.at(foo)'
   mutation 'self.fetch(foo)'
+  mutation 'self.key?(foo)'
   mutation 'foo'
 end
 
@@ -444,6 +447,7 @@ Mutant::Meta::Example.add do
   mutation 'foo[]'
   mutation 'foo.at(*bar)'
   mutation 'foo.fetch(*bar)'
+  mutation 'foo.key?(*bar)'
   mutation 'foo[nil]'
   mutation 'foo[self]'
   mutation 'foo[bar]'