Update for change in const lint name.

ehuss · ehuss · commit 8c0d76bc42a4 · 2020-02-21T09:30:42.000-08:00
diff --git a/src/expressions/array-expr.md b/src/expressions/array-expr.md
@@ -62,7 +62,7 @@ in a _panicked state_ if it fails.
 
 ```rust,should_panic
 // lint is deny by default.
-#![warn(const_err)]
+#![warn(unconditional_panic)]
 
 ([1, 2, 3, 4])[2];        // Evaluates to 3
 
