switch to upstream rowan's API

crates/ra_syntax/src/ast/extensions.rs

@@ -24,10 +24,7 @@ impl ast::NameRef {
 }
 
 fn text_of_first_token(node: &SyntaxNode) -> &SmolStr {
-    match node.0.green().children().first() {
-        Some(rowan::GreenElement::Token(it)) => it.text(),
-        _ => panic!(),
-    }
+    node.green().children().first().and_then(|it| it.as_token()).unwrap().text()
 }
 
 impl ast::Attr {