Test gcc6 cmake3.13

.travis.yml

@@ -79,6 +79,19 @@ before_install:
   - source .travis/common.sh
 
 install:
+  - DEPS_DIR="${HOME}/deps"
+  - mkdir -p ${DEPS_DIR} && cd ${DEPS_DIR}
+  - |
+    if [[ "${TRAVIS_OS_NAME}" == "linux" ]]; then
+      CMAKE_URL="https://cmake.org/files/v3.13/cmake-3.13.0-rc3-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}
+      echo ${PATH}
+    else
+      brew install cmake || brew upgrade cmake
+    fi
+  - cmake --version
+  - cd -
   - .travis/install.sh
 
 script: