install cmake from mason / simplify install

.travis.yml

@@ -116,19 +116,16 @@ before_install:
   - source ./scripts/install_node.sh 4
   - npm install
   - DEPS_DIR="${TRAVIS_BUILD_DIR}/deps"
-  - mkdir -p ${DEPS_DIR} && cd ${DEPS_DIR}
+  - export PATH=${DEPS_DIR}/bin:${PATH} && mkdir -p ${DEPS_DIR}
+  - CMAKE_URL="https://mason-binaries.s3.amazonaws.com/${TRAVIS_OS_NAME}-x86_64/cmake/3.5.2.tar.gz"
+  - travis_retry wget --quiet -O - ${CMAKE_URL} | tar --strip-components=1 -xz -C ${DEPS_DIR}
   - |
-    if [[ "${TRAVIS_OS_NAME}" == "linux" ]]; then
-      CMAKE_URL="http://www.cmake.org/files/v3.5/cmake-3.5.1-Linux-x86_64.tar.gz"
-      mkdir cmake && travis_retry wget --quiet -O - ${CMAKE_URL} | tar --strip-components=1 -xz -C cmake
-      export PATH=${DEPS_DIR}/cmake/bin:${PATH}
-    elif [[ "${TRAVIS_OS_NAME}" == "osx" ]]; then
+    if [[ "${TRAVIS_OS_NAME}" == "osx" ]]; then
       # implicit deps, but seem to be installed by default with recent images: libxml2 GDAL boost
-      brew install cmake libzip libstxxl lua51 luabind tbb md5sha1sum ccache
+      brew install libzip libstxxl lua51 luabind tbb md5sha1sum ccache
     fi
 
 install:
-  - cd ${TRAVIS_BUILD_DIR}
   - |
     if [[ "${TRAVIS_OS_NAME}" == "linux" ]]; then
       ./scripts/check_taginfo.py taginfo.json profiles/car.lua