Update yaml files to confirm to yamllint

1 job for master in 17 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Test
failed build #1075

00:00:17

 
Name Stage Failure
failed
build Test There is an unknown failure, please try again
Pulling docker image league/haskell-stack:20180605 ...
ERROR: Preparation failed: Error: No such image: league/haskell-stack:20180605
Will be retried in 3s ...
Using Docker executor with image league/haskell-stack:20180605 ...
Using docker image sha256:6ab6779d4437d934f6af79c40989dcd47986002aab8e0f0cd9b3888c0b2948c2 for predefined container...
Pulling docker image league/haskell-stack:20180605 ...
ERROR: Preparation failed: Error: No such image: league/haskell-stack:20180605
Will be retried in 3s ...
ERROR: Job failed (system failure): Error: No such image: league/haskell-stack:20180605