Avoid use of method chaining in provenance spec

This unifies behavior across all Ruby versions, so we don't need
the complex conditional.

spec/extensions/provenance_spec.rb

@@ -5,25 +5,17 @@
  @ds = Sequel.mock.dataset.extension(:provenance)
  end
 
- line = __LINE__ + 2
+ line = __LINE__ + 1
  def ds
- @ds.
-  from(:t).
-  select(:a).
-  where(:c)
+ ds = @ds.from(:t)
+ ds = ds.select(:a)
+ ds = ds.where(:c)
+ ds
  end
 
- if RUBY_ENGINE == 'jruby' && RUBY_VERSION >= '3.1'
- line1 = line2 = line3 = line + 3
- elsif RUBY_ENGINE == 'jruby' && RUBY_VERSION < '2.6'
- line1 = line2 = line3 = line
- elsif RUBY_VERSION >= '2'
- line1 = line+1
- line2 = line+2
- line3 = line+3
- else
- line1 = line2 = line3 = line
- end
+ line1 = line+1
+ line2 = line+2
+ line3 = line+3
 
  it "should not include provenance comment if there is no comment" do
  @ds.sql.must_equal 'SELECT *'