Add g++ 4.8, OS X -std=c++1z to Travis

.travis.yml

@@ -27,6 +27,15 @@ matrix:
     - env: BOGUS_JOB=true
 
   include:
+    - os: linux
+      env: TOOLSET=gcc COMPILER=g++-4.8 CXXSTD=c++11
+      addons:
+        apt:
+          packages:
+            - g++-4.8
+          sources:
+            - ubuntu-toolchain-r-test
+
     - os: linux
       env: TOOLSET=gcc COMPILER=g++-4.9 CXXSTD=c++11
       addons:
@@ -177,6 +186,9 @@ matrix:
     - os: osx
       env: TOOLSET=clang COMPILER=clang++ CXXSTD=c++14
 
+    - os: osx
+      env: TOOLSET=clang COMPILER=clang++ CXXSTD=c++1z
+
 install:
   - cd ..
   - git clone -b $TRAVIS_BRANCH --depth 1 https://github.com/boostorg/boost.git boost-root