fix travis build with swift 3.1

.travis.yml

@@ -1,10 +1,12 @@
 os:
   - linux
-  - osx
 language: generic
 sudo: required
 dist: trusty
-osx_image: xcode8.1
+services: 
+  - docker
+
+before_install:
+  - docker build -t bson .  
 script:
-  - eval "$(curl -sL https://raw.githubusercontent.com/OpenKitten/Mongo-Assets/master/bson-travisci)"  
-  - eval "$(curl -sL https://raw.githubusercontent.com/OpenKitten/Mongo-Assets/master/codecov)"
+  - docker run --rm --name bson_test bson  

Dockerfile

@@ -0,0 +1,10 @@
+FROM swiftdocker/swift:3.1
+
+
+WORKDIR /code
+
+COPY Package.swift /code/
+COPY ./Tests /code/Tests
+COPY ./Sources /code/Sources
+
+CMD swift test