In 1.8.7, Object#methods returns an array of strings

Luckily, we already have some code in this very file that handles that
situation, so we can just ride along.

lib/rspec/matchers/built_in/has.rb

@@ -51,7 +51,7 @@ def description
         # queries `has_receiveddd?`, the spy _fakes_ the method, returning its (truthy) self.
         def really_responds_to?(method)
           if defined?(RSpec::Mocks::Double) && @actual.is_a?(RSpec::Mocks::Double)
-            @actual.respond_to?(method) && @actual.methods.include?(method)
+            @actual.respond_to?(method) && methods_include?(method)
           else
             @actual.respond_to?(method)
           end
@@ -70,11 +70,19 @@ def predicate_accessible?
           def private_predicate?
             @actual.private_methods.include? predicate.to_s
           end
+
+          def methods_include?(method)
+            @actual.methods.include?(method.to_s)
+          end
           # :nocov:
         else
           def private_predicate?
             @actual.private_methods.include? predicate
           end
+
+          def methods_include?(method)
+            @actual.methods.include?(method)
+          end
         end
 
         def predicate_result