presets:
  travis:
    # Travis is sloooow.
    timeout: 3x

presets:
  travis:
    # Travis is sloooow.
    timeout: 3x

    # Pub has a huge number of small suites, which means test is frequently
    # loading new ones. Keeping concurrency low helps limit load timeouts.
    concurrency: 4

Use low concurrency on Travis.
Use low concurrency on Travis.

4 is just a guess here.
