Add record literal syntax (#326)

crates/nu-command/src/core_commands/do_.rs

@@ -33,9 +33,9 @@ impl Command for Do {
         call: &Call,
         input: PipelineData,
     ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
-        let block_id = call.positional[0]
-            .as_block()
-            .expect("internal error: expected block");
+        let block: Value = call.req(engine_state, stack, 0)?;
+        let block_id = block.as_block()?;
+
         let rest: Vec<Value> = call.rest(engine_state, stack, 1)?;
 
         let block = engine_state.get_block(block_id);