Resolve Bundler's deprecation warning

[purinkle]

Currently, the script returns the following deprecation warning

[DEPRECATED] Using the `config` command without a subcommand [list, get, set,
unset] is deprecated and will be removed in the future. Use `bundle config set
--global jobs 11` instead.

We want to respond to any warnings as soon as possible to reduce the likelihood of the script breaking

We could resolve this by updating the call to Bundler's config command