[TRAVIS] Compile using default gcc (4.8)

.travis.yml

@@ -2,22 +2,11 @@ language: cpp
 dist: trusty
 sudo: required
 cache: ccache
-before_install:
-- eval "${MATRIX_EVAL}"
-- ${CXX} --version
 install: travis/install_deps.sh
 script: travis/compile.sh
 env:
-  global:
-    - MATRIX_EVAL="CC=gcc-5 && CXX=g++-5"
   matrix:
     - PLATFORM="native_static"
     - PLATFORM="native_dyn"
     - PLATFORM="win32_static"
     - PLATFORM="win32_dyn"
-addons:
-  apt:
-    sources:
-      - ubuntu-toolchain-r-test
-    packages:
-      - g++-5