fix travis

.travis.yml

@@ -15,6 +15,14 @@ branches:
     - master
     - develop
 
+# g++-5 also needed for clang to see C++14 stdlib
+addons:
+  apt:
+    sources:
+      - ubuntu-toolchain-r-test
+    packages:
+      - g++-5
+
 matrix:
   include:
     - os: linux
@@ -26,14 +34,8 @@ matrix:
     - os: osx
       env: SERIAL=OFF
     - os: linux # coverage build
-      addons:
-        apt:
-          sources:
-            - ubuntu-toolchain-r-test
-          packages:
-            - g++-5
       compiler: gcc
-      env: GCOV=gcov-5 CC=gcc-5 CXX=g++-5
+      env: GCOV=gcov CC=gcc-5 CXX=g++-5
 
 git:
   depth: 1