rename is_missing? to missing?

lib/scoruby/predicates/compound_predicate.rb

@@ -23,14 +23,14 @@ def true?(features)
         and?(features) if @boolean_operator == 'and'
       end
 
-      def is_missing?(features)
+      def missing?(features)
         @field.any? {|f| !features.keys.include?(f)}
       end
 
       private
 
       def surrogate?(features)
-        return @predicates[1].true?(features) if @predicates[0].is_missing?(features)
+        return @predicates[1].true?(features) if @predicates[0].missing?(features)
         @predicates[0].true?(features)
       end
 

lib/scoruby/predicates/false_predicate.rb

@@ -11,7 +11,7 @@ def true?(_)
         false
       end
 
-      def is_missing?(_)
+      def missing?(_)
         false
       end
     end

lib/scoruby/predicates/simple_predicate.rb

@@ -29,7 +29,7 @@ def true?(features)
         features[field].nil? || !features.has_key?(field) if @operator == IS_MISSING
       end
 
-      def is_missing?(features)
+      def missing?(features)
         !features.keys.include?(@field)
       end
 

lib/scoruby/predicates/simple_set_predicate.rb

@@ -19,7 +19,7 @@ def true?(features)
         @array.include? features[@field] if @operator == IS_IN
       end
 
-      def is_missing?(features)
+      def missing?(features)
         !features.keys.include?(@field)
       end
 

lib/scoruby/predicates/true_predicate.rb

@@ -11,7 +11,7 @@ def true?(_)
         true
       end
 
-      def is_missing?(_)
+      def missing?(_)
         false
       end
     end