fix: fix typo in help message.

Author: smeghead

bin/php-class-diagram

@@ -50,7 +50,7 @@ OPTIONS
       --disable-class-name-summary describe classname without Class summary of document comment.
       --php5                       parse php source file as php5.
       --php7                       parse php source file as php7.
-      --php8                       parse php source file as php8. (not suppoted)
+      --php8                       parse php source file as php8. (not supported)
       --header='header string'     additional header string. You can specify multiple header values.
       --include='wildcard'         include target file pattern. (default: `*.php`) You can specify multiple include patterns.
       --exclude='wildcard'         exclude target file pattern. You can specify multiple exclude patterns.