Improve performance (#49)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

index.js

@@ -1,9 +1,14 @@
 import ansiRegex from 'ansi-regex';
 
+const regex = ansiRegex();
+
 export default function stripAnsi(string) {
 	if (typeof string !== 'string') {
 		throw new TypeError(`Expected a \`string\`, got \`${typeof string}\``);
 	}
 
-	return string.replace(ansiRegex(), '');
+	// Even though the regex is global, we don't need to reset the `.lastIndex`
+	// because unlike `.exec()` and `.test()`, `.replace()` does it automatically
+	// and doing it manually has a performance penalty.
+	return string.replace(regex, '');
 }