Convert stragging BN type imports (#3595)

packages/api-derive/src/staking/erasHistoric.ts

@@ -1,13 +1,12 @@
 // Copyright 2017-2021 @polkadot/api-derive authors & contributors
 // SPDX-License-Identifier: Apache-2.0
 
+import type BN from 'bn.js';
 import type { ApiInterfaceRx } from '@polkadot/api/types';
 import type { Option, u32 } from '@polkadot/types';
 import type { ActiveEraInfo, EraIndex } from '@polkadot/types/interfaces';
 import type { Observable } from '@polkadot/x-rxjs';
 
-import BN from 'bn.js';
-
 import { map } from '@polkadot/x-rxjs/operators';
 
 import { memo } from '../util';

packages/api-derive/src/staking/stakerRewards.ts

@@ -1,14 +1,13 @@
 // Copyright 2017-2021 @polkadot/api-derive authors & contributors
 // SPDX-License-Identifier: Apache-2.0
 
+import type BN from 'bn.js';
 import type { ApiInterfaceRx } from '@polkadot/api/types';
 import type { AccountId, EraIndex, StakingLedger } from '@polkadot/types/interfaces';
 import type { Observable } from '@polkadot/x-rxjs';
 import type { DeriveEraPoints, DeriveEraPrefs, DeriveEraRewards, DeriveEraValPrefs, DeriveStakerExposure, DeriveStakerReward, DeriveStakerRewardValidator } from '../types';
 import type { DeriveStakingQuery } from './types';
 
-import BN from 'bn.js';
-
 import { BN_BILLION, BN_ZERO } from '@polkadot/util';
 import { combineLatest, of } from '@polkadot/x-rxjs';
 import { map, switchMap } from '@polkadot/x-rxjs/operators';