Fix missing word in opening sentence (#969)

Author: ryanjbonnell

docs/rules/html-closing-bracket-newline.md

@@ -10,7 +10,7 @@ description: require or disallow a line break before tag's closing brackets
 - :gear: This rule is included in `"plugin:vue/strongly-recommended"` and `"plugin:vue/recommended"`.
 - :wrench: The `--fix` option on the [command line](https://eslint.org/docs/user-guide/command-line-interface#fixing-problems) can automatically fix some of the problems reported by this rule.
 
-People have own preference about the location of closing brackets.
+People have their own preference about the location of closing brackets.
 This rule enforces a line break (or no line break) before tag's closing brackets.
 
 ```html