Feature gate: 1.16.0 instead of 1.15.0

src/libsyntax/feature_gate.rs

@@ -323,7 +323,7 @@ pub fn new() -> Features {
     (active, abi_ptx, "1.15.0", None),
 
     // The `i128` type
-    (active, i128_type, "1.15.0", Some(35118)),
+    (active, i128_type, "1.16.0", Some(35118)),
 );
 
 declare_features! (