Fix around blocks

Author: johnnyshields

spec/mongoid/fields/field_types_spec.rb

@@ -5,10 +5,9 @@
 describe Mongoid::Fields::FieldTypes do
 
   around do |example|
-    mapping = described_class::DEFAULT_MAPPING.dup
-    described_class.instance_variable_set(:@mapping, mapping)
+    described_class.instance_variable_set(:@mapping, described_class::DEFAULT_MAPPING.dup)
     example.run
-    described_class.instance_variable_set(:@mapping, mapping)
+    described_class.instance_variable_set(:@mapping, described_class::DEFAULT_MAPPING.dup)
   end
 
   describe '.get' do

spec/mongoid/fields_spec.rb

@@ -1789,10 +1789,9 @@ class DiscriminatorChild2 < DiscriminatorParent
     context '.type method' do
       around do |example|
         klass = Mongoid::Fields::FieldTypes
-        mapping = klass::DEFAULT_MAPPING.dup
-        klass.instance_variable_set(:@mapping, mapping)
+        klass.instance_variable_set(:@mapping, klass::DEFAULT_MAPPING.dup)
         example.run
-        klass.instance_variable_set(:@mapping, mapping)
+        klass.instance_variable_set(:@mapping, klass::DEFAULT_MAPPING.dup)
       end
 
       it 'can define a custom type' do