Fix builds on travis

Author: wiktorn

.gitmodules

@@ -0,0 +1,4 @@
+[submodule "pybind11"]
+	path = contrib/pybind11
+	url = https://github.com/pybind/pybind11
+	branch = master

.travis.yml

@@ -23,17 +23,16 @@ matrix:
         - os: linux
           compiler: gcc
           env: USE_PYTHON_VERSION=3
-
 # http://docs.travis-ci.com/user/apt/
 addons:
     apt:
         sources:
             - boost-latest
+            - ubuntu-toolchain-r-test
         packages:
-            - g++-4.8
-            - gcc-4.8
-            - libboost-python1.55-dev
+            - g++-6
             - libboost1.55-dev
+            - libproj-dev
             - libsparsehash-dev
             - python-dev
             - python-nose
@@ -55,8 +54,8 @@ install:
 
 script:
     - if [ "${CXX}" = 'g++' ]; then
-          CXX=g++-4.8;
-          CC=gcc-4.8;
+          CXX=g++-6;
+          CC=gcc-6;
       fi
     - if [ "$TRAVIS_OS_NAME" = 'osx' ]; then
           PYTHON=python${USE_PYTHON_VERSION};