Remove the gem update from .travis.yml

It has no effect on deployment error and may cause further network issues.

Author: kennytm

.travis.yml

@@ -301,7 +301,6 @@ before_deploy:
           rm -rf obj/build/dist/doc &&
           cp -r obj/build/dist/* deploy/$TRAVIS_COMMIT;
       fi
-  - travis_retry gem update --system
   - ls -la deploy/$TRAVIS_COMMIT
 
 deploy: