Force gem update --system before deployment.

kennytm · kennytm · commit 9cfdabaf3ca6 · 2017-11-06T03:53:41.000+08:00
Try to prevent #44159.
diff --git a/.travis.yml b/.travis.yml
@@ -286,6 +286,7 @@ before_deploy:
           rm -rf obj/build/dist/doc &&
           cp -r obj/build/dist/* deploy/$TRAVIS_COMMIT;
       fi
+  - travis_retry gem update --system
 
 deploy:
   - provider: s3
