Use Xcode 9.3 and OS X 10.13 image on Travis-CI

.travis.yml

@@ -4,19 +4,19 @@ dist: trusty
 os:
   - osx
 
-osx_image: xcode9.2
+osx_image: xcode9.3
 
 compiler:
   - clang
 
 env:
   - MACOSX_DEPLOYMENT_TARGET=10.8
-    VERSIONER_PERL_VERSION=5.16
+    VERSIONER_PERL_VERSION=5.18
     VERSIONER_PYTHON_VERSION=2.7
     vi_cv_path_python=/usr/bin/python
     vi_cv_path_python3=/usr/local/bin/python3
     vi_cv_path_plain_lua=/usr/local/bin/lua
-    vi_cv_dll_name_perl=/System/Library/Perl/5.16/darwin-thread-multi-2level/CORE/libperl.dylib
+    vi_cv_dll_name_perl=/System/Library/Perl/5.18/darwin-thread-multi-2level/CORE/libperl.dylib
     vi_cv_dll_name_python=/System/Library/Frameworks/Python.framework/Versions/2.7/Python
     vi_cv_dll_name_python3=/usr/local/Frameworks/Python.framework/Versions/3.6/Python
     VIMCMD=src/MacVim/build/Release/MacVim.app/Contents/MacOS/Vim