Fix for #302 / #296 conflict (#303)

I merged #296 thinking I would rebase #302 but before I could it was
merged.

This just renames BigInt -> BigInteger in the new BigInt tests
introduced in #296 which was done before the #302 renaming.

chain/rust/src/utils.rs

@@ -596,18 +596,18 @@ mod tests {
     #[test]
     fn bigint_uint_u128_min() {
         let bytes = [0x00];
-        let x = BigInt::from_cbor_bytes(&bytes).unwrap();
+        let x = BigInteger::from_cbor_bytes(&bytes).unwrap();
         assert_eq!(bytes, x.to_cbor_bytes().as_slice());
         assert_eq!(x.as_u128(), Some(u128::MIN));
         assert_eq!(x.to_string(), "0");
     }
 
     #[test]
     fn bigint_uint_u128_max() {
-        let bytes = BigInt::from_str(&u128::MAX.to_string())
+        let bytes = BigInteger::from_str(&u128::MAX.to_string())
             .unwrap()
             .to_cbor_bytes();
-        let x = BigInt::from_cbor_bytes(&bytes).unwrap();
+        let x = BigInteger::from_cbor_bytes(&bytes).unwrap();
         assert_eq!(bytes, x.to_cbor_bytes().as_slice());
         assert_eq!(x.as_u128(), Some(u128::MAX));
         assert_eq!(x.to_string(), "340282366920938463463374607431768211455");