Switch characters in URL-safe Base64 to use tilde (~) for padding

The tilde character is less familiar to most users and harder to type
on most keyboards (compared to the hyphen and underscore characters).

src/Base64.php

@@ -11,7 +11,7 @@ namespace Delight\Auth;
 final class Base64 {
 
 	const SPECIAL_CHARS_ORIGINAL = '+/=';
-	const SPECIAL_CHARS_SAFE = '~_-';
+	const SPECIAL_CHARS_SAFE = '_-~';
 
 	public static function encode($data, $safeChars = false) {
 		$result = base64_encode($data);