Suppress `warning: BigDecimal.new is deprecated`

`BigDecimal.new` has been deprecated in BigDecimal 1.3.3
 which will be a default for Ruby 2.5.

Refer
https://github.com/ruby/bigdecimal/commit/533737338db915b00dc7168c3602e4b462b23503

* This commit has been made as follows:

```
cd rails
git grep -l BigDecimal.new | grep -v guides/source/5_0_release_notes.md | grep -v activesupport/test/xml_mini_test.rb | xargs sed -i -e "s/BigDecimal.new/BigDecimal/g"
```
- `activesupport/test/xml_mini_test.rb`
Editmanually to remove `.new` and `::`

- guides/source/5_0_release_notes.md
This is a Rails 5.0 release notes.

1 files changed, 3 insertions, 3 deletions

diff --git a/activesupport/test/core_ext/array/conversions_test.rb b/activesupport/test/core_ext/array/conversions_test.rb
index 0f919efcb0..0a7c43d421 100644
--- a/activesupport/test/core_ext/array/conversions_test.rb
+++ b/activesupport/test/core_ext/array/conversions_test.rb
@@ -90,7 +90,7 @@ class ToXmlTest < ActiveSupport::TestCase
   def test_to_xml_with_hash_elements
     xml = [
       { name: "David", age: 26, age_in_millis: 820497600000 },
-      { name: "Jason", age: 31, age_in_millis: BigDecimal.new("1.0") }
+      { name: "Jason", age: 31, age_in_millis: BigDecimal("1.0") }
     ].to_xml(skip_instruct: true, indent: 0)
 
     assert_equal '<objects type="array"><object>', xml.first(30)
@@ -173,7 +173,7 @@ class ToXmlTest < ActiveSupport::TestCase
   def test_to_xml_with_instruct
     xml = [
       { name: "David", age: 26, age_in_millis: 820497600000 },
-      { name: "Jason", age: 31, age_in_millis: BigDecimal.new("1.0") }
+      { name: "Jason", age: 31, age_in_millis: BigDecimal("1.0") }
     ].to_xml(skip_instruct: false, indent: 0)
 
     assert_match(/^<\?xml [^>]*/, xml)
@@ -183,7 +183,7 @@ class ToXmlTest < ActiveSupport::TestCase
   def test_to_xml_with_block
     xml = [
       { name: "David", age: 26, age_in_millis: 820497600000 },
-      { name: "Jason", age: 31, age_in_millis: BigDecimal.new("1.0") }
+      { name: "Jason", age: 31, age_in_millis: BigDecimal("1.0") }
     ].to_xml(skip_instruct: true, indent: 0) do |builder|
       builder.count 2
     end