Travis-CI: Add macOS to build matrix using Miniconda

.travis.yml

-language: python
+os: linux
 dist: trusty
 sudo: false
 
+addons:
+  apt:
+    packages:
+      - gdb
+      - python-dbg
+      - python3-dbg
+
 cache:
   pip: true
   directories:
     - $HOME/.ccache
 
+language: python
 python:
   - 2.7
   - 3.6
@@ -30,17 +38,67 @@ env:
     - BACKEND=c
     - BACKEND=cpp
 
+matrix:
+  include:
+    - os: osx
+      osx_image: xcode6.4
+      env: BACKEND=c PY=2
+      python: 2
+      language: c
+      compiler: clang
+      cache: false
+    - os: osx
+      osx_image: xcode6.4
+      env: BACKEND=cpp PY=2
+      python: 2
+      language: cpp
+      compiler: clang
+      cache: false
+    - os: osx
+      osx_image: xcode6.4
+      env: BACKEND=c PY=3
+      python: 3
+      language: c
+      compiler: clang
+      cache: false
+    - os: osx
+      osx_image: xcode6.4
+      env: BACKEND=cpp PY=3
+      python: 3
+      language: cpp
+      compiler: clang
+      cache: false
+  allow_failures:
+    - python: pypy
+    - python: pypy3
+    - python: 3.6-dev
+    - python: 3.7-dev
+  exclude:
+    - python: pypy
+      env: BACKEND=cpp
+    - python: pypy3
+      env: BACKEND=cpp
+
 branches:
   only:
     - master
     - release
 
+before_install:
+  - |
+    if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then # Install Miniconda
+      curl -s -o miniconda.sh https://repo.continuum.io/miniconda/Miniconda$PY-latest-MacOSX-x86_64.sh;
+      bash miniconda.sh -b -p $HOME/miniconda && rm miniconda.sh;
+      export PATH="$HOME/miniconda/bin:$PATH"; hash -r;
+      #conda install --quiet --yes nomkl --file=test-requirements.txt --file=test-requirements-cpython.txt;
+    fi
+
 install:
   - python -c 'import sys; print("Python %s" % (sys.version,))'
   - if [ -n "${TRAVIS_PYTHON_VERSION##*-dev}" -a -n "${TRAVIS_PYTHON_VERSION##2.6*}" ]; then pip install -r test-requirements.txt $( [ -z "${TRAVIS_PYTHON_VERSION##pypy*}" ] || echo " -r test-requirements-cpython.txt" ) ; fi
   - CFLAGS="-O2 -ggdb -Wall -Wextra $(python -c 'import sys; print("-fno-strict-aliasing" if sys.version_info[0] == 2 else "")')" python setup.py build
 
-before_script: ccache -s
+before_script: ccache -s || true
 
 script:
   - PYTHON_DBG="python$( python -c 'import sys; print("%d.%d" % sys.version_info[:2])' )-dbg"
@@ -48,22 +106,3 @@ script:
   - if [ false && "$BACKEND" = "cpp" ]; then pip install pythran; fi  # disabled: needs Pythran > 0.8.1
   - CFLAGS="-O2 -ggdb -Wall -Wextra $(python -c 'import sys; print("-fno-strict-aliasing" if sys.version_info[0] == 2 else "")')" python setup.py build_ext -i
   - CFLAGS="-O0 -ggdb -Wall -Wextra" python runtests.py -vv -x Debugger --backends=$BACKEND -j7
-
-matrix:
-  allow_failures:
-    - python: pypy
-    - python: pypy3
-    - python: 3.6-dev
-    - python: 3.7-dev
-  exclude:
-    - python: pypy
-      env: BACKEND=cpp
-    - python: pypy3
-      env: BACKEND=cpp
-
-addons:
-  apt:
-    packages:
-      - gdb
-      - python-dbg
-      - python3-dbg