Fixed wrong variable name in SampleCrowdsale.test.js. (#916)

test/examples/SampleCrowdsale.test.js

@@ -76,7 +76,7 @@ contract('SampleCrowdsale', function ([owner, wallet, investor]) {
   });
 
   it('should reject payments after end', async function () {
-    await increaseTimeTo(this.afterEnd);
+    await increaseTimeTo(this.afterClosingTime);
     await this.crowdsale.send(ether(1)).should.be.rejectedWith(EVMRevert);
     await this.crowdsale.buyTokens(investor, { value: ether(1), from: investor }).should.be.rejectedWith(EVMRevert);
   });