Update travis file

.travis.yml

@@ -22,14 +22,20 @@ matrix:
     - os: linux
       arch: arm64
       name: "Linux / GCC (Debug)"
+      before_install:
+        - sudo apt-get remove cmake
+        - wget https://cmake.org/files/v3.8/cmake-3.8.2.tar.gz
+        - tar xf cmake-3.8.2.tar.gz
+        - cd cmake-3.8.2
+        - ./configure
+        - sudo make install
+        - cmake --version
       addons:
         apt:
           sources:
             - ubuntu-toolchain-r-test
-            - sourceline: 'ppa:george-edison55/cmake-3.x'
           packages:
             - g++-8
-            - cmake
       env:
         - MATRIX_EVAL="CC=gcc-8 && CXX=g++-8" BUILD_TYPE="Debug" DOUBLE_PRECISION="False"