Recognize Nextflow files as Groovy files

Nextflow is a domain specific language (DSL) implemented on top of the Groovy programming language
https://www.nextflow.io/

lib/rouge/lexers/groovy.rb

@@ -7,11 +7,13 @@ class Groovy < RegexLexer
       title "Groovy"
       desc 'The Groovy programming language (http://www.groovy-lang.org/)'
       tag 'groovy'
-      filenames '*.groovy', 'Jenkinsfile', '*.Jenkinsfile'
+      aliases 'nextflow', 'nf'
+      filenames '*.groovy', 'Jenkinsfile', '*.Jenkinsfile', '*.nf'
       mimetypes 'text/x-groovy'
 
       def self.detect?(text)
         return true if text.shebang?(/groovy/)
+        return true if text.shebang?(/nextflow/)
       end
 
       def self.keywords

spec/lexers/groovy_spec.rb

@@ -11,10 +11,16 @@
       assert_guess :filename => 'foo.groovy'
       assert_guess :filename => 'Jenkinsfile'
       assert_guess :filename => 'foo.Jenkinsfile'
+      assert_guess :filename => 'foo.nf'
     end
 
     it 'guesses by mimetype' do
       assert_guess :mimetype => 'text/x-groovy'
     end
+
+    it "guesses by source" do
+      assert_guess :source => "#!/usr/bin/env groovy"
+      assert_guess :source => "#!/usr/bin/env nextflow"
+    end
   end
 end