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, 1 insertions, 1 deletions

diff --git a/actionpack/test/controller/parameters/parameters_permit_test.rb b/actionpack/test/controller/parameters/parameters_permit_test.rb
index ebdaca0162..e9b94b056b 100644
--- a/actionpack/test/controller/parameters/parameters_permit_test.rb
+++ b/actionpack/test/controller/parameters/parameters_permit_test.rb
@@ -59,7 +59,7 @@ class ParametersPermitTest < ActiveSupport::TestCase
 
   test "key: permitted scalar values" do
     values  = ["a", :a, nil]
-    values += [0, 1.0, 2**128, BigDecimal.new(1)]
+    values += [0, 1.0, 2**128, BigDecimal(1)]
     values += [true, false]
     values += [Date.today, Time.now, DateTime.now]
     values += [STDOUT, StringIO.new, ActionDispatch::Http::UploadedFile.new(tempfile: __FILE__),