Fix default bonding duration (#267)

Related https://github.com/paritytech/substrate/issues/2288

Someone needs to update the value in Alex testnet

polkadot/service/src/chain_spec.rs

@@ -110,7 +110,7 @@ fn staging_testnet_config_genesis() -> GenesisConfig {
 			current_session_reward: 0,
 			validator_count: 7,
 			sessions_per_era: 12,
-			bonding_duration: 60 * MINUTES,
+			bonding_duration: 12,
 			offline_slash_grace: 4,
 			minimum_validator_count: 4,
 			stakers: initial_authorities.iter().map(|x| (x.0.clone(), x.1.clone(), STASH, StakerStatus::Validator)).collect(),
@@ -253,7 +253,7 @@ pub fn testnet_genesis(
 			minimum_validator_count: 1,
 			validator_count: 2,
 			sessions_per_era: 5,
-			bonding_duration: 2 * 60 * 12,
+			bonding_duration: 12,
 			offline_slash: Perbill::zero(),
 			session_reward: Perbill::zero(),
 			current_session_reward: 0,