fix enum discriminants not being included in the hash

tests/derive_test.rs

@@ -1,3 +1,4 @@
+use std::hash::{Hash, Hasher};
 use hash2::Hash2;
 
 #[derive(Hash2)]
@@ -49,6 +50,13 @@ where
     ref2: &'b str,
 }
 
+#[derive(Hash2)]
+enum ScalerEnum {
+    A,
+    B,
+    C,
+}
+
 #[derive(Hash2)]
 enum SimpleEnum {
     A,
@@ -141,6 +149,21 @@ fn test_complex() {
     let _ = hash_value(&s);
 }
 
+#[test]
+fn test_scaler_enum() {
+    let e1 = ScalerEnum::A;
+    let e2 = ScalerEnum::B;
+    let e3 = ScalerEnum::C;
+
+    let a = hash_value(&e1);
+    let b = hash_value(&e2);
+    let c = hash_value(&e3);
+    assert_ne!(a, b);
+    assert_ne!(a, c);
+    assert_ne!(b, c);
+}
+
+
 #[test]
 fn test_simple_enum() {
     let e1 = SimpleEnum::A;