message: [ci] Remove stable and beta channels
  This should improve CI build times a bit.
  Note that currently all of pDSL is nightly only anyway.
diff: @@ -4,14 +4,14 @@ dist: trusty
  sudo: true
  rust:
  - - stable
  - - beta
  + # - stable
  + # - beta
  - nightly
  -matrix:
  - allow_failures:
  - - rust: stable
  - - rust: beta
  +# matrix:
  +# allow_failures:
  +# - rust: stable
  +# - rust: beta
  env:
  global:
  