[ci] added 2 more osx images to the travis build matrix (xcode 9 and 9.1)
diff --git a/.travis.yml b/.travis.yml
index 50d9864..cafdabd 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -215,6 +215,16 @@
       osx_image: xcode8.3
       os: osx
 
+    # Xcode 9 Clang
+    - env: COMPILER=clang++ HAS_ASAN_32=true HAS_UBSAN_32=true HAS_ASAN_64=true HAS_UBSAN_64=true
+      osx_image: xcode9
+      os: osx
+
+    # Xcode 9.1 Clang
+    - env: COMPILER=clang++ HAS_ASAN_32=true HAS_UBSAN_32=true HAS_ASAN_64=true HAS_UBSAN_64=true
+      osx_image: xcode9.1
+      os: osx
+
     # OSX GCC 4.6
     - env: COMPILER=g++-4.6
       compiler: gcc