minor fix for allow to compile without persy dependency

src/error.rs

@@ -1,4 +1,3 @@
-use persy::PersyError;
 use ruma::{
     api::client::{
         error::{Error as RumaError, ErrorKind},
@@ -9,6 +8,9 @@ use ruma::{
 use thiserror::Error;
 use tracing::warn;
 
+#[cfg(feature = "persy")]
+use persy::PersyError;
+
 #[cfg(feature = "conduit_bin")]
 use {
     crate::RumaResponse,
@@ -141,6 +143,7 @@ where
     }
 }
 
+#[cfg(feature = "persy")]
 impl<T: Into<PersyError>> From<persy::PE<T>> for Error {
     fn from(err: persy::PE<T>) -> Self {
         Error::PersyError {