Update Travis to Mono 4.7 nightly on OSX.

.travis.yml

@@ -20,7 +20,7 @@ install:
   - if [ "$TRAVIS_OS_NAME" = "linux" ]; then sudo apt-get update -qq; fi
   - if [ "$TRAVIS_OS_NAME" = "linux" ]; then sudo apt-get install -y mono-devel; fi
   - if [ "$TRAVIS_OS_NAME" = "osx" ]; then brew install wget xz; fi
-  - if [ "$TRAVIS_OS_NAME" = "osx" ]; then wget -O mono.pkg http://download.mono-project.com/archive/4.4.2/macos-10-universal/MonoFramework-MDK-4.4.2.11.macos10.xamarin.universal.pkg; fi
+  - if [ "$TRAVIS_OS_NAME" = "osx" ]; then wget -O mono.pkg http://download.mono-project.com/archive/nightly/macos-10-universal/MonoFramework-MDK-4.7.0.215.macos10.xamarin.universal.pkg; fi
   - if [ "$TRAVIS_OS_NAME" = "osx" ]; then sudo installer -pkg "mono.pkg" -target /; fi
   - if [ "$TRAVIS_OS_NAME" = "linux" ] && [ "$CXX" = "g++" ]; then export CXX="g++-4.8" CC="gcc-4.8"; fi