Only splat class/symbol matcher block return value if it returns array

This fixes issues when having the blocks return objects that
respond to to_a.

lib/roda/plugins/_symbol_class_matchers.rb

@@ -92,7 +92,11 @@ def _merge_matcher_blocks(type, obj, block, matcher_meth)
 
               proc do |*a|
                 if captures = send(matcher_meth, *a)
-                  send(convert_meth, *captures)
+                  if captures.is_a?(Array)
+                    send(convert_meth, *captures)
+                  else
+                    send(convert_meth, captures)
+                  end
                 end
               end
             else

spec/plugin/class_matchers_spec.rb

@@ -152,6 +152,17 @@ def klass9.to_s; "klass9" end
     body("/1000000000000000000001").must_equal ""
   end
 
+  it "yields hash instances as single arguments" do
+    app(:class_matchers) do |r|
+      r.is('a', Array){|h| h.to_a.join(',')}
+      r.is('h', Hash){|h| h.to_a.join('-')}
+    end
+    app.class_matcher(Hash, /(\w)(\w)/){|k,v| {k=>v}}
+    app.class_matcher(Array, Hash){|h| h['c'] = 'd'; h }
+    body('/h/ab').must_equal 'a-b'
+    body('/a/ab').must_equal 'a,b,c,d'
+  end
+
   it "freezes :class_matchers option when freezing app" do
     app(:class_matchers){|r| }
     app.freeze