title: Cypress soaking up all available memory
body: <p>I'm having serious issues with Cypress soaking up all my available memory (16Gb). I have 30+ tests and if I attempt to run them through the UI all at once then Cypress gradually uses all my available memory and then typically fails with a test timeout error. Closing the Cypress UI always recovers all the memory. I've seen <a href="https://github.com/cypress-io/cypress/issues/431" rel="noreferrer">https://github.com/cypress-io/cypress/issues/431</a> which suggests setting <code>numTestsKeptInMemory</code> to 0 but this makes no difference, also running in headless mode with <code>cypress run</code> makes no difference either: Ultimately all my memory get soaked up. </p>
  
  <p>Also during development of the tests I've been using <code>it.only</code> but even when running only one test at a time the memory gradually gets soaked up until restarting Cypress is needed.</p>
  
  <p>I'm using Cypress 1.4.1 on Ubuntu 16.04 (elementaryOS Loki)</p>
  
  <p>Does anyone else have the same trouble?</p>