travis build also with clang

.travis.yml

@@ -8,7 +8,12 @@ sudo: false
 language:
   - cpp
 
-addons:
+matrix:
+  include:
+    - env: COMPILER_VERSION=4.8
+      os: linux
+      compiler: g++
+      addons:
         apt:
           sources:
           - ubuntu-toolchain-r-test
@@ -18,9 +23,20 @@ addons:
           - g++-4.8
           - cmake
           - libglib2.0-dev
+    - env: COMPILER_VERSION=3.5
+      os: linux
+      compiler: clang++
+      addons:
+        apt:
+          sources:
+          - ubuntu-toolchain-r-test
+          - kalakris-cmake
+          - ubuntu-sdk-team
+          packages:
+          - clang-3.5
+          - cmake
+          - libglib2.0-dev
 
-env:
-- COMPILER_VERSION=4.8
 
 before_script:
   - mkdir build