doc: use sentence case for class property

Change the one instance of the Class Property heading in our docs to
Class property to match style with other headers.

PR-URL: #35540
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

doc/api/buffer.md

@@ -765,7 +765,7 @@ console.log(Buffer.isEncoding(''));
 // Prints: false
 ```
 
-### Class Property: `Buffer.poolSize`
+### Class property: `Buffer.poolSize`
 <!-- YAML
 added: v0.11.3
 -->

tools/doc/json.js

@@ -437,7 +437,7 @@ const eventPrefix = '^Event: +';
 const classPrefix = '^[Cc]lass: +';
 const ctorPrefix = '^(?:[Cc]onstructor: +)?`?new +';
 const classMethodPrefix = '^Static method: +';
-const maybeClassPropertyPrefix = '(?:Class Property: +)?';
+const maybeClassPropertyPrefix = '(?:Class property: +)?';
 
 const maybeQuote = '[\'"]?';
 const notQuotes = '[^\'"]+';