fix: Rubocop offenses

Author: hsinn0

app/models/runtime/feature_flag.rb

@@ -90,7 +90,7 @@ def self.override_default_flags(feature_flag_overrides)
       invalid_keys = feature_flag_overrides.keys.to_set - FeatureFlag::DEFAULT_FLAGS.keys.to_set
       raise "Invalid feature flag name(s): #{invalid_keys.to_a}" if invalid_keys.any?
 
-      invalid_values = feature_flag_overrides.select { |k,v| !v.in? [true,false] }
+      invalid_values = feature_flag_overrides.reject { |_, v| v.is_a?(TrueClass) || v.is_a?(FalseClass) }
       raise "Invalid feature flag value(s): #{invalid_values}" if invalid_values.any?
 
       feature_flag_overrides.each do |flag_name, flag_value|

spec/unit/models/runtime/feature_flag_spec.rb

@@ -294,28 +294,28 @@ module VCAP::CloudController
           feature_flag_overrides = { an_invalid_name: true }
           expect do
             FeatureFlag.override_default_flags(feature_flag_overrides)
-          end.to raise_error("Invalid feature flag name(s): [:an_invalid_name]")
+          end.to raise_error('Invalid feature flag name(s): [:an_invalid_name]')
         end
 
         it 'raises an error for a mix of valid and invalid names' do
           feature_flag_overrides = { diego_docker: true, an_invalid_name: true }
           expect do
             FeatureFlag.override_default_flags(feature_flag_overrides)
-          end.to raise_error("Invalid feature flag name(s): [:an_invalid_name]")
+          end.to raise_error('Invalid feature flag name(s): [:an_invalid_name]')
         end
 
         it 'raises an error for all invalid names' do
           feature_flag_overrides = { invalid_name1: true, invalid_name2: false }
           expect do
             FeatureFlag.override_default_flags(feature_flag_overrides)
-          end.to raise_error("Invalid feature flag name(s): [:invalid_name1, :invalid_name2]")
+          end.to raise_error('Invalid feature flag name(s): [:invalid_name1, :invalid_name2]')
         end
 
         it 'raises an error for invalid values' do
           feature_flag_overrides = { diego_docker: 'an invalid value', user_org_creation: false }
           expect do
             FeatureFlag.override_default_flags(feature_flag_overrides)
-          end.to raise_error("Invalid feature flag value(s): {:diego_docker=>\"an invalid value\"}")
+          end.to raise_error('Invalid feature flag value(s): {:diego_docker=>"an invalid value"}')
         end
       end