Fix rspec deprecation warning

Fixes warning:

Using should from rspec-expectations' old :should syntax without explicitly enabling the syntax is deprecated. Use the new :expect syntax or explicitly enable :should with config.expect_with(:rspec) { |c| c.syntax = :should } instead. Called from /Users/jacobvosmaer/Desktop/gitlab-development-kit/go-gitlab-shell/src/gitlab.com/gitlab-org/gitlab-shell/spec/hooks_utils_spec.rb:6:in `block (2 levels) in <top (required)>'.