fix linter error

(cherry picked from commit c12a1c6898c5db300bfeceea50438b328601705d)

test/token/ERC20/behaviors/ERC20Capped.behavior.js

@@ -1,5 +1,4 @@
 const { expectThrow } = require('../../../helpers/expectThrow');
-const expectEvent = require('../../../helpers/expectEvent');
 
 const BigNumber = web3.BigNumber;