ethash: fix test (#3925)

Author: jochem-brouwer

packages/ethash/test/miner.spec.ts

@@ -75,7 +75,7 @@ describe('Miner', () => {
     const blockMiner = e.getMiner(block)
     const blockSolution = <Block>await blockMiner.mine(-1)
 
-    assert.isTrue(e.verifyPOW(blockSolution))
+    assert.isTrue(await e.verifyPOW(blockSolution))
   }, 60000)
 
   it('Check if it is possible to stop the miner', async () => {