Shorten slot time for simulator

lighthouse/environment/src/lib.rs

@@ -170,7 +170,7 @@ pub struct Environment<E: EthSpec> {
     runtime: Runtime,
     log: Logger,
     eth_spec_instance: E,
-    eth2_config: Eth2Config,
+    pub eth2_config: Eth2Config,
 }
 
 impl<E: EthSpec> Environment<E> {

tests/beacon_chain_sim/src/main.rs

@@ -28,6 +28,8 @@ fn simulation(num_nodes: usize, validators_per_node: usize) -> Result<(), String
         .multi_threaded_tokio_runtime()?
         .build()?;
 
+    env.eth2_config.spec.milliseconds_per_slot = 2_000;
+
     let mut base_config = testing_client_config();
 
     let now = SystemTime::now()