Add a === b -> a.is_a?(b) mutation

- Closes #689
  * NOTE: I have gone with `is_a?` over `kind_of?` because [this is more commonly used](https://github.com/rubocop-hq/ruby-style-guide#is-a-vs-kind-of)

Changelog.md

@@ -1,5 +1,10 @@
 # Unreleased
 
+
+* [#1188](https://github.com/mbj/mutant/pull/1188)
+
+  Add `a === b` -> `a.is_a?(b)` mutation
+
 * [#1189](https://github.com/mbj/mutant/pull/1189)
 
   * Add mutation from `=~` -> `#match?`

lib/mutant/mutator/node/send.rb

@@ -17,6 +17,7 @@ class Send < self
           :< =>          %i[== eql? equal?],
           :<= =>         %i[< == eql? equal?],
           :== =>         %i[eql? equal?],
+          :=== =>        %i[is_a?],
           :=~ =>         %i[match?],
           :> =>          %i[== eql? equal?],
           :>= =>         %i[> == eql? equal?],

meta/send.rb

@@ -562,7 +562,7 @@
   mutation 'foo(n..-2)'
 end
 
-(Mutant::AST::Types::BINARY_METHOD_OPERATORS - %i[=~ <= >= < > == != eql?]).each do |operator|
+(Mutant::AST::Types::BINARY_METHOD_OPERATORS - %i[=~ <= >= < > == === != eql?]).each do |operator|
   Mutant::Meta::Example.add :send do
     source "true #{operator} false"
 
@@ -729,3 +729,17 @@
   mutation 'foo'
   mutation 'foo(a__mutant__: nil)'
 end
+
+Mutant::Meta::Example.add :send do
+  source 'a === b'
+
+  singleton_mutations
+
+  mutation 'a'
+  mutation 'b'
+  mutation 'nil === b'
+  mutation 'self === b'
+  mutation 'a === nil'
+  mutation 'a === self'
+  mutation 'a.is_a?(b)'
+end