Update .travis.yml to use xcode8.2

Author: kevinchalet

.travis.yml

@@ -1,5 +1,5 @@
 language: csharp
-sudo: required
+sudo: false
 dist: trusty
 addons:
   apt:
@@ -18,6 +18,7 @@ mono: none
 os:
   - linux
   - osx
+osx_image: xcode8.2
 before_install:
   - if test "$TRAVIS_OS_NAME" == "osx"; then brew update; brew install openssl; ln -s /usr/local/opt/openssl/lib/libcrypto.1.0.0.dylib /usr/local/lib/; ln -s /usr/local/opt/openssl/lib/libssl.1.0.0.dylib /usr/local/lib/; fi
 script: