[PAN-3160] Rinkeby Istanbul fork block (#35)

The Rinkeby Fork Block for Istanbul is 5435345, targeting 13 Nov 2019.

As announced by the Rinkeby maintainers here: https://twitter.com/peter_szilagyi/status/1174580897980592129

Signed-off-by: Danno Ferrin <danno.ferrin@gmail.com>

config/src/main/resources/rinkeby.json

@@ -9,6 +9,7 @@
     "byzantiumBlock": 1035301,
     "constantinopleBlock": 3660663,
     "constantinopleFixBlock": 4321234,
+    "istanbulBlock":  5435345,
     "clique": {
       "blockperiodseconds": 15,
       "epochlength": 30000

ethereum/core/src/test/java/org/hyperledger/besu/ethereum/mainnet/MainnetProtocolScheduleTest.java

@@ -131,7 +131,7 @@ public class MainnetProtocolScheduleTest {
     Assertions.assertThat(sched.getByBlockNumber(3_660_663L).getName()).isEqualTo("Constantinople");
     Assertions.assertThat(sched.getByBlockNumber(4_321_234L).getName())
         .isEqualTo("ConstantinopleFix");
-    Assertions.assertThat(sched.getByBlockNumber(Long.MAX_VALUE).getName())
-        .isEqualTo("ConstantinopleFix");
+    Assertions.assertThat(sched.getByBlockNumber(5_435_345L).getName()).isEqualTo("Istanbul");
+    Assertions.assertThat(sched.getByBlockNumber(Long.MAX_VALUE).getName()).isEqualTo("Istanbul");
   }
 }