change BlockHashCount parameter (#1086)

runtime/common/src/lib.rs

@@ -51,7 +51,7 @@ pub use impls::{CurrencyToVoteHandler, TargetedFeeAdjustment, ToAuthor};
 pub type NegativeImbalance<T> = <balances::Module<T> as Currency<<T as system::Trait>::AccountId>>::NegativeImbalance;
 
 parameter_types! {
-	pub const BlockHashCount: BlockNumber = 250;
+	pub const BlockHashCount: BlockNumber = 2400;
 	pub const MaximumBlockWeight: Weight = 2 * WEIGHT_PER_SECOND;
 	pub const AvailableBlockRatio: Perbill = Perbill::from_percent(75);
 	pub const MaximumBlockLength: u32 = 5 * 1024 * 1024;