veloren fails to build with rust 1.59.0

error log:

error: format argument must be a string literal
    --> voxygen/src/hud/diary.rs:1263:49
     |
1263 |                         unknown => unreachable!(unknown),
     |                                                 ^^^^^^^
     |
help: you might be missing a string literal to format with
     |
1263 |                         unknown => unreachable!("{}", unknown),
     |                                                 +++++

the fix:

@@ -1260,7 +1260,7 @@ impl<'a> Widget for Diary<'a> {
                                 (None, None) => String::new(),
                             }
                         },
-                        unknown => unreachable!(unknown),
+                        unknown => unreachable!("unknown"),
                     };
 
                     let mut number = Text::new(&value)