[macOS] Switch CI to Xcode 8.2

.travis.yml

@@ -1,7 +1,7 @@
 os:
  - linux
  - osx
-osx_image: xcode7.3
+osx_image: xcode8.2
 language: cpp
 sudo: required
 dist: trusty

CI/before_script.osx.sh

@@ -12,7 +12,7 @@ cd build
 cmake \
 -D CMAKE_PREFIX_PATH="$DEPENDENCIES_ROOT;$QT_PATH" \
 -D CMAKE_OSX_DEPLOYMENT_TARGET="10.8" \
--D CMAKE_OSX_SYSROOT="macosx10.11" \
+-D CMAKE_OSX_SYSROOT="macosx10.12" \
 -D CMAKE_BUILD_TYPE=Debug \
 -D OPENMW_OSX_DEPLOYMENT=TRUE \
 -D DESIRED_QT_VERSION=5 \