Update Travis deployment rule to reflect Xcode 10.2 version change

Author: ychin

.travis.yml

@@ -76,7 +76,7 @@ deploy:
   file: src/MacVim/build/Release/MacVim.dmg
   skip_cleanup: true
   on:
-    condition: $TRAVIS_OSX_IMAGE = xcode10.1
+    condition: $TRAVIS_OSX_IMAGE = xcode10.2
     all_branches: true
     tags: true
     repo: macvim-dev/macvim