Quick fix union return types

The recent introduction of support for intersection types broke union
return types, because at the time these are actually rendered, the
current separator (`::$type_separator`) is already reset to null.  This
quick fix merely works for union types; I'll come up with a proper fix
for both union and intersection types ASAP.

phpdotnet/phd/Package/PHP/XHTML.php

@@ -448,7 +448,7 @@ public function format_methodsynopsis($open, $name, $attrs, $props) {
                 }
                 $types[] = '<span class="type">' . $formatted_type . '</span>';
             }
-            $type = implode($this->type_separator, $types);
+            $type = implode("|", $types);
             if (count($types) > 1) {
                 $type = '<span class="type">' . $type . '</span>';
             }