Change the expectation for predicate methods

Predicate methods typically return true or false, and should only exist
for the uncountable and discrete, e.g. `use_transactional_fixtures?`,
but not `max_formatted_output_length?`.

This relates to changes made in rspec/rspec-core#2736

spec/rspec/rails/configuration_spec.rb

@@ -23,13 +23,18 @@
     opts ||= {}
     default_value = opts[:default]
     alias_setting = opts[:alias_with]
-    query_method = "#{accessor}?".to_sym
+    query_method = accessor
+    predicate_method = "#{accessor}?".to_sym
     command_method = "#{accessor}=".to_sym
 
     specify "`##{query_method}` is `#{default_value.inspect}` by default" do
       expect(config.send(query_method)).to be(default_value)
     end
 
+    specify "`##{predicate_method}` is `#{!!default_value}` by default" do
+      expect(config.send(predicate_method)).to be(!!default_value)
+    end
+
     describe "`##{command_method}`" do
       it "changes `#{query_method}` to the provided value" do
         expect {