Fix typo

src/lib.rs

@@ -241,7 +241,7 @@ where
                 }
 
                 if let Err(e) =
-                    self.tx_step(tx_buf.expect("We've transmitting but there's no tx buf"))
+                    self.tx_step(tx_buf.expect("We're transmitting but there's no tx buf"))
                 {
                     // something went wrong. Go back to idle
                     self.state = InternalState::Idle;