fix: make mock-agent.js test more resilient (nodejs#2780)

Author: Uzlopak

test/mock-agent.js

@@ -789,7 +789,7 @@ test('MockAgent - handle delays to simulate work', async (t) => {
 
   const response = await getResponse(body)
   t.strictEqual(response, 'hello')
-  const elapsedInMs = process.hrtime(start)[1] / 1e6
+  const elapsedInMs = Math.ceil(process.hrtime(start)[1] / 1e6)
   t.ok(elapsedInMs >= 50, `Elapsed time is not greater than 50ms: ${elapsedInMs}`)
 })