updated the panic message wording

src/libstd/thread/local.rs

@@ -237,7 +237,7 @@ impl<T: 'static> LocalKey<T> {
     pub fn with<F, R>(&'static self, f: F) -> R
                       where F: FnOnce(&T) -> R {
         self.try_with(f).expect("cannot access a Thread Local Storage value \
-                                 during or after it is destroyed")
+                                 during or after destruction")
     }
 
     /// Acquires a reference to the value in this TLS key.