NEWS.md: fixed lists and indents [ci skip]

* The definition lists extensions of the RDoc Markdown parser does
  not support nesting.

* The RDoc Markdown parser requires more indents for nested lists.

NEWS.md

@@ -16,11 +16,12 @@ sufficient information, see the ChangeLog file or Redmine
 
 ### Core classes updates (outstanding ones only)
 
-Hash::
+* Hash
 
-  Modified method::
+    * Modified method
 
-    * Hash#transform_keys now accepts a hash that maps keys to new keys.  [Feature #16274]
+        * Hash#transform_keys now accepts a hash that maps keys to new
+          keys.  [Feature #16274]
 
 ### Stdlib updates (outstanding ones only)
 
@@ -28,13 +29,13 @@ Hash::
 
 * Regexp literals are frozen [Feature #8948] [Feature #16377]
 
-```
-/foo/.frozen? #=> true
-```
+    ```
+    /foo/.frozen? #=> true
+    ```
 
 * The bundled gems
 
-  * net-telnet and xmlrpc has been removed from the bundled gems.
+    net-telnet and xmlrpc has been removed from the bundled gems.
     If you interested in the maintain them, Please comment your plan
     to https://github.com/ruby/xmlrpc or https://github.com/ruby/net-telnet.