message: Update stable builds to rust 1.39
diff: @@ -11,7 +11,7 @@ workflows:
  jobs:
  base:
  docker:
  - - image: rust:1.37
  + - image: rust:1.39
  steps:
  - checkout
  - run:
  @@ -69,7 +69,7 @@ jobs:
  cranelift_vm:
  docker:
  - - image: rust:1.37
  + - image: rust:1.39
  steps:
  - checkout
  - run:
  