fix xcode move to 9.2

Author: xssss1

.travis.yml

@@ -35,12 +35,12 @@ matrix:
       - <<: *osx
         osx_image: xcode7.3
         env: CONAN_APPLE_CLANG_VERSIONS=7.3
-      - <<: *osx
-        osx_image: xcode8.1
-        env: CONAN_APPLE_CLANG_VERSIONS=8.0
       - <<: *osx
         osx_image: xcode8.3
         env: CONAN_APPLE_CLANG_VERSIONS=8.1
+      - <<: *osx
+        osx_image: xcode9.2
+        env: CONAN_APPLE_CLANG_VERSIONS=9.0
 
 install:
   - chmod +x .travis/install.sh