message: Disable code-coverage CI build.
  It's failing for non-obvious reasons and it hasn't been all that useful even when it does work.
diff: @@ -53,9 +53,6 @@ matrix:
  - os: linux
  env: CLIPPY=yes
  rust: nightly-2018-06-25
  - - os: linux
  - env: COVERAGE=yes GNUPLOT=yes
  - sudo: required
  - os: linux
  env: RUSTFMT=yes
  rust: nightly-2018-03-29
  