Merge pull request #912 from eax0r/travis-fix

fix Travis not running due to missing package repositories

.travis.yml

@@ -1,16 +1,21 @@
 language: c
+sudo: required
+dist: xenial
 
 os:
-    - linux
+  - linux
 
 compiler:
-    - gcc
-    - clang
+  - gcc
+  - clang
 
 before_install:
-    - if [ $TRAVIS_OS_NAME == linux ]; then sudo add-apt-repository -y ppa:pyglfw/pyglfw && sudo apt-get update -qq && sudo apt-get install -y --no-install-recommends libglfw3 libglfw3-dev libglew-dev; fi
+  - if [ $TRAVIS_OS_NAME == linux ]; then 
+      sudo apt-get update -qq;
+      sudo apt-get install -y --no-install-recommends libglfw3 libglfw3-dev libglew-dev;
+    fi
 
 script:
-    - make -C demo/glfw_opengl3 CFLAGS="-Wall -DINCLUDE_ALL"
-    - make -C demo/glfw_opengl2
-    - make -C example
+  - make -C demo/glfw_opengl2
+  - make -C demo/glfw_opengl3
+  - make -C example