Update .travis.yml

.travis.yml

@@ -2,16 +2,10 @@ dist: xenial
 os: linux
 language: c
 compiler: gcc
-addons:
+before_install:
-  apt:
+  - sudo apt-get -y update
-    sources:
+  - sudo apt-get -y install python3 gcc make
-      - ubuntu-toolchain-r-test
-    packages:
-      - gcc-7
-      - cmake
 script:
-  - sudo ln -s /usr/bin/gcc-6 /usr/local/bin/gcc
-  - export CC=gcc-7
   - python3 autogen.py
   - make coverage
 after_success: