Workaround for `bundle conflict` in AppVeyor
Workaround for `bundle conflict` in AppVeyor

Follow up of https://github.com/appveyor/ci/issues/1944#issuecomment-345496213

This is a workaround patch to AppVeyor config.
This change attempts to resolve the following error.

```console
gem install bundler --no-document
bundler's executable "bundle" conflicts with C:/Ruby23/bin/bundle
Overwrite the executable? [yN]
```

https://ci.appveyor.com/project/bbatsov/rubocop/build/1540/job/f8gxj2m6b53qe3tg#L23

This causes the job to fail with a timeout of 60 min.

> Build execution time has reached the maximum allowed time for your plan (60 minutes).

https://ci.appveyor.com/project/bbatsov/rubocop/build/1540/job/f8gxj2m6b53qe3tg/messages

This change attempt to solve by forcibly updating the bundler by adding
`--force` option.

panthomakos/rubocop,maxjacobson/rubocop,smakagon/rubocop,vergenzt/rubocop,petehamilton/rubocop,jfelchner/rubocop,tdeo/rubocop,akihiro17/rubocop,meganemura/rubocop,palkan/rubocop,akihiro17/rubocop,pocke/rubocop,panthomakos/rubocop,mikegee/rubocop,maxjacobson/rubocop,petehamilton/rubocop,jmks/rubocop,vergenzt/rubocop,tejasbubane/rubocop,rrosenblum/rubocop,pocke/rubocop,jfelchner/rubocop,tdeo/rubocop,mikegee/rubocop,smakagon/rubocop,rrosenblum/rubocop,rrosenblum/rubocop,tejasbubane/rubocop,sue445/rubocop,tejasbubane/rubocop,deivid-rodriguez/rubocop,vergenzt/rubocop,palkan/rubocop,scottmatthewman/rubocop,meganemura/rubocop,meganemura/rubocop,deivid-rodriguez/rubocop,bquorning/rubocop,urbanautomaton/rubocop,urbanautomaton/rubocop,jfelchner/rubocop,panthomakos/rubocop,bquorning/rubocop,akihiro17/rubocop,petehamilton/rubocop,bbatsov/rubocop,palkan/rubocop,haziqhafizuddin/rubocop,deivid-rodriguez/rubocop,maxjacobson/rubocop,sue445/rubocop,mikegee/rubocop,jmks/rubocop,haziqhafizuddin/rubocop,scottmatthewman/rubocop,sue445/rubocop,bquorning/rubocop,tdeo/rubocop,bbatsov/rubocop,jmks/rubocop