CMake URL fixed.

.travis.yml

@@ -63,7 +63,7 @@ install:
     - mkdir -p "${DEPENDENCY_DIR}" && cd "${DEPENDENCY_DIR}"
     - |
         if [[ ! -d "$(ls -A ${DEPENDENCY_DIR}/cmake)" ]]; then
-          CMAKE_URL="https://cmake.org/files/v3.6/cmake-3.8.2-Linux-x86_64.tar.gz"
+          CMAKE_URL="https://cmake.org/files/v3.8/cmake-3.8.2-Linux-x86_64.tar.gz"
           mkdir -p cmake && travis_retry wget --no-check-certificate --quiet -O - "${CMAKE_URL}" | tar --strip-components=1 -xz -C cmake
         fi
         export PATH="${DEPENDENCY_DIR}/cmake/bin:${PATH}"