Implement min_score option for function_score query

https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-function-score-query.html

Author: ChrisBr

lib/elasticsearch/dsl/search/queries/function_score.rb

@@ -35,6 +35,7 @@ class FunctionScore
           option_method :max_boost
           option_method :score_mode
           option_method :boost_mode
+          option_method :min_score
 
           def initialize(*args, &block)
             super

spec/elasticsearch/dsl/search/queries/function_score_spec.rb

@@ -121,6 +121,17 @@
         expect(search.to_hash[:function_score][:boost_mode]).to eq('bar')
       end
     end
+
+    describe '#min_scoore' do
+
+      before do
+        search.min_score('bar')
+      end
+
+      it 'applies the option' do
+        expect(search.to_hash[:function_score][:min_score]).to eq('bar')
+      end
+    end
   end
 
   describe '#initialize' do