disable g++4.9 build which gets killed / use clang 3.6 to prepare for c++14 support

.travis.yml

@@ -15,9 +15,9 @@ addons:
   apt:
     sources:
      - ubuntu-toolchain-r-test
-     - llvm-toolchain-precise-3.5
+     - llvm-toolchain-precise-3.6
     packages:
-     - clang-3.5
+     - clang-3.6
 
 cache:
   directories:
@@ -32,13 +32,15 @@ matrix:
         apt:
           sources: [ 'ubuntu-toolchain-r-test', 'llvm-toolchain-precise-3.6' ]
           packages: [ 'clang-3.6', 'libstdc++-4.9-dev', 'libstdc++6' ]
-    - os: linux
-      compiler: gcc
-      env: JOBS=6 CXX="ccache g++-4.9" CC="gcc-4.9"
-      addons:
-        apt:
-          sources: [ 'ubuntu-toolchain-r-test' ]
-          packages: [ 'gcc-4.9', 'g++-4.9', 'libstdc++-4.9-dev', 'libstdc++6' ]
+    # OOM killer knocking out build on render_markers_symbolizer.cpp
+    #
+    #- os: linux
+    #  compiler: gcc
+    #  env: JOBS=6 CXX="ccache g++-4.9" CC="gcc-4.9"
+    #  addons:
+    #    apt:
+    #      sources: [ 'ubuntu-toolchain-r-test' ]
+    #      packages: [ 'gcc-4.9', 'g++-4.9', 'libstdc++-4.9-dev', 'libstdc++6' ]
     - os: osx
       compiler: clang
       osx_image: xcode7 # upgrades clang from 6 -> 7