removed failing compilers

.travis.yml

@@ -4,14 +4,6 @@ sudo: false
 
 matrix:
   include:
-    - os: linux
-      compiler: gcc
-      addons:
-        apt:
-          sources: ['ubuntu-toolchain-r-test']
-          packages: ['g++-4.8', 'valgrind']
-      env: COMPILER=g++-4.8
-
     - os: linux
       compiler: gcc
       addons:
@@ -30,17 +22,6 @@ matrix:
           packages: ['g++-5', 'valgrind']
       env: COMPILER=g++-5
 
-    - os: linux
-      compiler: clang
-      env: COMPILER=clang++
-
-    - os: linux
-      compiler: clang
-      addons:
-        apt:
-          sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-precise-3.5']
-          packages: ['clang-3.5', 'valgrind']
-      env: COMPILER=clang++-3.5
 
     - os: linux
       compiler: clang