Update travis (#9)

* Update travis

.travis.yml

@@ -1,38 +1,90 @@
 sudo: required
-dist: precise
+dist: trusty
 language: cpp
 
 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++-5
-      env: COMPILER=g++-5
-    - compiler: clang
-      addons:
-        apt:
-          sources:
-            - ubuntu-toolchain-r-test
-            - llvm-toolchain-precise-3.5
-          packages:
-            - clang-3.5
-      env: COMPILER=clang++-3.5
 
-before_install:
-  - sudo apt-get update -qq
+    # Clang 4.0
+    - env: COMPILER=clang++-4.0
+      addons:
+        apt:
+          packages:
+            - clang-4.0
+            - g++-5
+          sources:
+            - ubuntu-toolchain-r-test
+            - llvm-toolchain-trusty-4.0
+
+    # Clang 5.0
+    - env: COMPILER=clang++-5.0
+      addons:
+        apt:
+          packages:
+            - clang-5.0
+            - g++-7
+          sources:
+            - ubuntu-toolchain-r-test
+            - llvm-toolchain-trusty-5.0
+
+    # Clang 6.0
+    - env: COMPILER=clang++-6.0
+      addons:
+        apt:
+          packages:
+            - clang-6.0
+            - g++-7
+          sources:
+            - ubuntu-toolchain-r-test
+            - llvm-toolchain-trusty-6.0
+
+    # Clang 7.0
+    - env: COMPILER=clang++-7
+      addons:
+        apt:
+          packages:
+            - clang-7
+            - g++-7
+          sources:
+            - ubuntu-toolchain-r-test
+            - sourceline: 'deb http://apt.llvm.org/trusty/ llvm-toolchain-trusty-7 main'
+              key_url: 'https://apt.llvm.org/llvm-snapshot.gpg.key'
+
+    # GCC 5
+    - env: COMPILER=g++-5
+      addons:
+        apt:
+          packages: g++-5
+          sources:
+            - ubuntu-toolchain-r-test
+
+    # GCC 6
+    - env: COMPILER=g++-6
+      addons:
+        apt:
+          packages: g++-6
+          sources:
+            - ubuntu-toolchain-r-test
+
+    # GCC 7
+    - env: COMPILER=g++-7
+      addons:
+        apt:
+          packages: g++-7
+          sources:
+            - ubuntu-toolchain-r-test
+
+install:
+    # Set the ${CXX} variable properly
+    - export CXX=${COMPILER}
+    - ${CXX} --version
+    # Travis machines have 2 cores
+    - JOBS=2
+before_script:
+    # have CMake generate build files
+    - cd "${TRAVIS_BUILD_DIR}"
+    - mkdir build && cd build
+    - cmake ..
 script:
-  - mkdir build
-  - cd build
-  - cmake -DCMAKE_CXX_COMPILER=$COMPILER .. && make
+    # build
+    - cmake --build . -- -j${JOBS}