Upgrade cmake on bots (#646)

 Upgrade cmake
diff --git a/kokoro/scripts/linux/build.sh b/kokoro/scripts/linux/build.sh
index f5cd478..86d0ec5 100644
--- a/kokoro/scripts/linux/build.sh
+++ b/kokoro/scripts/linux/build.sh
@@ -43,6 +43,13 @@
   BUILD_TYPE="RelWithDebInfo"
 fi
 
+# removing the old cmake version
+echo y | sudo apt-get purge --auto-remove cmake
+# install new cmake version
+echo y | sudo apt-get install cmake
+
+echo $(date): $(cmake --version)
+
 # Get ninja
 wget -q https://github.com/ninja-build/ninja/releases/download/v1.8.2/ninja-linux.zip
 unzip -q ninja-linux.zip