Oops, that wasn't as backwards compatible as I thought.

spec/jekyll_seo_tag_spec.rb

@@ -446,7 +446,7 @@ EOS
   end
 
   context 'with pagination' do
-    let(:context) { make_context(environments: { 'paginator' => paginator }) }
+    let(:context) { make_context({}, { 'paginator' => paginator }) }
 
     it 'outputs pagination links' do
       expect(output).to match(%r{<link rel="prev" href="foo">})

spec/spec_helper.rb

@@ -38,6 +38,6 @@ def make_site(options = {})
   Jekyll::Site.new(config)
 end
 
-def make_context(registers = {}, environments: {})
+def make_context(registers = {}, environments = {})
   Liquid::Context.new(environments, {}, { site: site, page: page }.merge(registers))
 end