Try to install higher version of cmake on travis.

.travis.yml

@@ -11,7 +11,7 @@ matrix:
       osx_image: xcode9.2
 
 script:
-  - find / | grep cmake
+  - sudo rm -rf /usr/local/cmake-3.9.2 && sudo rm -rf /usr/local/cmake
   - wget https://cmake.org/files/v3.12/cmake-3.12.0-rc2-Linux-x86_64.sh
   - chmod +x cmake-3.12.0-rc2-Linux-x86_64.sh
   - sudo ./cmake-3.12.0-rc2-Linux-x86_64.sh --skip-license --exclude-subdir --prefix=/usr/local