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/guides/source/active_support_core_extensions.md b/guides/source/active_support_core_extensions.md
index 66d2fbd939..8e2826bb85 100644
--- a/guides/source/active_support_core_extensions.md
+++ b/guides/source/active_support_core_extensions.md
@@ -1978,19 +1978,19 @@ Extensions to `BigDecimal`
 The method `to_s` provides a default specifier of "F". This means that a simple call to `to_s` will result in floating point representation instead of engineering notation:
 
 ```ruby
-BigDecimal.new(5.00, 6).to_s       # => "5.0"
+BigDecimal(5.00, 6).to_s       # => "5.0"
 ```
 
 and that symbol specifiers are also supported:
 
 ```ruby
-BigDecimal.new(5.00, 6).to_s(:db)  # => "5.0"
+BigDecimal(5.00, 6).to_s(:db)  # => "5.0"
 ```
 
 Engineering notation is still supported:
 
 ```ruby
-BigDecimal.new(5.00, 6).to_s("e")  # => "0.5E1"
+BigDecimal(5.00, 6).to_s("e")  # => "0.5E1"
 ```
 
 Extensions to `Enumerable`