Remove .travis.yml due to switching to github actions.

.travis.yml

@@ -1,34 +0,0 @@
-language: cpp
-sudo: required
-dist: trusty
-
-os:
-  - linux
-  - osx
-
-compiler:
-  - gcc
-  - clang
-
-before_install:
-  - if [ $TRAVIS_OS_NAME == linux ]; then 
-      sudo apt-get update -qq;
-      sudo apt-get install -y --no-install-recommends libxrandr-dev libxi-dev libxxf86vm-dev libsdl2-dev;
-      wget https://github.com/glfw/glfw/releases/download/3.2.1/glfw-3.2.1.zip;
-      unzip glfw-3.2.1.zip && cd glfw-3.2.1; 
-      cmake -DBUILD_SHARED_LIBS=true -DGLFW_BUILD_EXAMPLES=false -DGLFW_BUILD_TESTS=false -DGLFW_BUILD_DOCS=false .;
-      sudo make -j $CPU_NUM install && cd ..;
-    fi
-  - if [ $TRAVIS_OS_NAME == osx ]; then 
-      brew update;
-      brew install glfw3;
-      brew install sdl2;
-    fi
-
-script: 
-  - make -C examples/example_glfw_opengl2
-  - make -C examples/example_glfw_opengl3
-  - make -C examples/example_sdl_opengl3
-  - if [ $TRAVIS_OS_NAME == osx ]; then 
-      xcodebuild -project examples/example_apple_metal/example_apple_metal.xcodeproj -target example_apple_metal_macos;
-    fi