remove unneeded field

src/logline.rs

@@ -64,7 +64,6 @@ pub struct Exception {
     pub exception: String,
     pub file: String,
     pub line: usize,
-    pub previous: Option<Box<Exception>>,
 }
 
 impl Hash for Exception {

src/matcher.rs

@@ -267,7 +267,6 @@ fn test_matcher() {
                     exception: "Bar\\FooException".into(),
                     file: "short".into(),
                     line: 68,
-                    previous: None,
                 }),
                 time: OffsetDateTime::now_utc(),
                 index: 0,