Fix Bundler 2 issue

[godrei]

Bundler 2 auto switches to Bundler 1 if Gemfile.lock selects Bundler 1. To do so Bundler 1 version needs to be installed.

Test test_xcode_11_ccertificate is running on Edge stack, as the issue came in that environment, see the CI builds.

[sadlerjw]

@godrei Hi there, this change has broken my build with the error:

ERROR: Error installing bundler:
"bundle" from bundler conflicts with /Users/vagrant/.rbenv/versions/2.6.5/bin/bundle

(I am still using the Xcode 11.2.x stack, not Xcode 11.3.x)
Reverting to version 1.5.0 of this step solved the problem.

From the comments in #106 it suggests that using --force in the gem install line added in this PR would fix the issue and allow both versions of bundler to co-exist. (Although I am a Ruby neophyte, I might be misunderstanding something.)

[cathyharmon]

We are aware of this issue and are currently working to get it corrected. Until it is fixed, please try the following workaround:

• Use the 1.5.0 version of the iOS Auto Provision step (you can select this as an input to the step in the workflow editor)

• Add a script step prior to the iOS Auto Provision step to install bundler 1.17.3. The script step should have 'gem install bundler --force -v 1.17.3`

So sorry for the inconvenience!

[sadlerjw]

No worries, thanks for looking into it :)