Improved travisCI support

.travis.yml

@@ -1,48 +1,49 @@
 language: cpp
 
-os:
-  - linux
-  - osx
-
 matrix:
   include:
-    - compiler: gcc
-      addons:
-        apt:
-          sources:
-            - ubuntu-toolchain-r-test
-          packages:
-            - g++-4.9
-      env: COMPILER=g++-4.9
-    - compiler: gcc
-      addons:
-        apt:
-          sources:
-            - ubuntu-toolchain-r-test
-          packages:
-            - g++-7
-      env: COMPILER=g++-7
-    - compiler: clang
-      addons:
-        apt:
-          sources:
-            - ubuntu-toolchain-r-test
-            - llvm-toolchain-precise-3.6
-          packages:
-            - clang-3.6
-      env:
-        - MATRIX_EVAL="CC=clang-3.6 && CXX=clang++-3.6"
-    - compiler: clang
-      addons:
-        apt:
-          sources:
-            - llvm-toolchain-trusty-5.0
-          packages:
-            - clang-5.0
-      env:
-        - MATRIX_EVAL="CC=clang-5.0 && CXX=clang++-5.0"
+    - os: linux
+      - compiler: gcc
+        addons:
+          apt:
+            sources:
+              - ubuntu-toolchain-r-test
+            packages:
+              - g++-4.9
+        env:
+          - MATRIX_EVAL="CC=gcc-4.9 && CXX=g++-4.9"
+      - compiler: gcc
+        addons:
+          apt:
+            sources:
+              - ubuntu-toolchain-r-test
+            packages:
+              - g++-7
+        env:
+          - MATRIX_EVAL="CC=gcc-7 && CXX=g++-7"
+    - os: osx
+      - compiler: clang
+        addons:
+          apt:
+            sources:
+              - ubuntu-toolchain-r-test
+              - llvm-toolchain-precise-3.6
+            packages:
+              - clang-3.6
+        env:
+          - MATRIX_EVAL="CC=clang-3.6 && CXX=clang++-3.6"
+      - compiler: clang
+        addons:
+          apt:
+            sources:
+              - llvm-toolchain-trusty-5.0
+            packages:
+              - clang-5.0
+        env:
+          - MATRIX_EVAL="CC=clang-5.0 && CXX=clang++-5.0"
 
-before_script: 
+before_install:
+    - eval "${MATRIX_EVAL}"
 
 script:
 - cmake --version