Stabilize blank_lines_upper_bound

Configurations.md

@@ -181,7 +181,7 @@ lines are found, they are trimmed down to match this integer.
 
 - **Default value**: `1`
 - **Possible values**: any non-negative integer
-- **Stable**: No (tracking issue: [#3381](https://github.com/rust-lang/rustfmt/issues/3381))
+- **Stable**: Yes
 
 ### Example
 Original Code:

src/config.rs

@@ -127,7 +127,7 @@ create_config! {
         "How to handle trailing commas for lists";
     match_block_trailing_comma: bool, false, true,
         "Put a trailing comma after a block based match arm (non-block arms are not affected)";
-    blank_lines_upper_bound: usize, 1, false,
+    blank_lines_upper_bound: usize, 1, true,
         "Maximum number of blank lines which can be put between items";
     blank_lines_lower_bound: usize, 0, false,
         "Minimum number of blank lines which must be put between items";