Fix adding explicit dyn

Author: eldruin

src/error.rs

@@ -29,7 +29,7 @@ impl ::std::error::Error for Error {
         }
     }
 
-    fn cause(&self) -> Option<&::std::error::Error> {
+    fn cause(&self) -> Option<&dyn (::std::error::Error)> {
         match *self {
             Error::Io(ref e) => Some(e),
             _ => None,