Install cmake from repositories for Ubuntu

Ubuntu 18.04 already has cmake 3.10.2

.travis/linux/docker.sh

 #!/bin/bash -ex
 
 apt-get update
-apt-get install -y build-essential git libqt5opengl5-dev libsdl2-dev libssl-dev python qtbase5-dev wget ninja-build
-
-# Get a recent version of CMake
-wget https://cmake.org/files/v3.10/cmake-3.10.1-Linux-x86_64.sh
-sh cmake-3.10.1-Linux-x86_64.sh --exclude-subdir --prefix=/ --skip-license
+apt-get install --no-install-recommends -y build-essential git libqt5opengl5-dev libsdl2-dev libssl-dev python qtbase5-dev wget cmake ninja-build
 
 cd /yuzu