message: Removing all clang builds as they don't support C++17?
diff: @@ -25,51 +25,6 @@ matrix:
  - g++-7
  env:
  - MATRIX_EVAL="CC=gcc-7 && CXX=g++-7"
  - - os: linux
  - addons:
  - apt:
  - sources:
  - - llvm-toolchain-trusty-3.6
  - packages:
  - - clang-3.6
  - env:
  - - MATRIX_EVAL="CC=clang-3.6 && CXX=clang++-3.6"
  - - os: linux
  - addons:
  - apt:
  - sources:
  - - llvm-toolchain-trusty-3.8
  - packages:
  - - clang-3.8
  - env:
  - - MATRIX_EVAL="CC=clang-3.8 && CXX=clang++-3.8"
  - - os: linux
  - addons:
  - apt:
  - sources:
  - - llvm-toolchain-trusty-3.9
  - packages:
  - - clang-3.9
  - env:
  - - MATRIX_EVAL="CC=clang-3.9 && CXX=clang++-3.9"
  - - os: linux
  - addons:
  - apt:
  - sources:
  - - llvm-toolchain-trusty-4.0
  - packages:
  - - clang-4.0
  - env:
  - - MATRIX_EVAL="CC=clang-4.0 && CXX=clang++-4.0"
  - - os: linux
  - addons:
  - apt:
  - sources:
  - - llvm-toolchain-trusty-5.0
  - packages:
  - - clang-5.0
  - env:
  - - MATRIX_EVAL="CC=clang-5.0 && CXX=clang++-5.0"
  - os: osx
  osx_image: xcode8
  env:
  