Add backporterd boost1.58 for building of mmap-object

- caused by allenluce/mmap-object#14
- which is transitively caused by mapbox/node-pre-gyp#361

.travis.yml

@@ -19,6 +19,11 @@ before_install:
   - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then unzip protoc-3.5.1-linux-x86_64.zip -d $HOME/protoc3; fi
   - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then curl -OL https://github.com/google/protobuf/releases/download/v3.5.1/protoc-3.5.1-osx-x86_64.zip; fi
   - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then unzip protoc-3.5.1-osx-x86_64.zip -d $HOME/protoc3; fi
+  # Remove after either bug in node-pre-gyp () is fixed or we get rid of mmap-object
+  - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then sudo add-apt-repository -y ppa:kzemek/boost; fi
+  - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then sudo apt-get update -qq; fi
+  - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then sudo apt-get install libboost1.58-dev; fi
+  # END Remove after either bug in node-pre-gyp () is fixed or we get rid of mmap-object
   - export PATH=$HOME/protoc3/bin:$PATH
   # Install yarn
   - curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version 1.5.1