Travis: Install CMake differently and support OS X

.travis.yml

@@ -6,9 +6,18 @@ compiler:
   - gcc
   - clang
 install:
-  - sudo add-apt-repository --yes ppa:george-edison55/cmake-3.x
+  ############################################################################
-  - sudo apt-get update --yes
+  # Install a recent CMake (unless already installed on OS X)
-  - sudo apt-get upgrade --yes
+  # See http://stackoverflow.com/questions/33196136/travis-ci-update-cmake-using-the-packages-cache
+  ############################################################################
+  - |
+    if [[ "${TRAVIS_OS_NAME}" == "linux" ]]; then
+      CMAKE_URL="http://www.cmake.org/files/v3.5/cmake-3.5.2-Linux-x86_64.tar.gz"
+      mkdir cmake && travis_retry wget --no-check-certificate --quiet -O - ${CMAKE_URL} | tar --strip-components=1 -xz -C cmake
+      export PATH=${DEPS_DIR}/cmake/bin:${PATH}
+    else
+      if ! brew ls --version cmake &>/dev/null; then brew install cmake; fi
+    fi
   - make install_deps
   - source setup.bash
 script: