adding description of return value [ci skip]

actionview/lib/action_view/template.rb

@@ -141,7 +141,7 @@ def initialize(source, identifier, handler, details)
       @compile_mutex     = Mutex.new
     end
 
-    # Returns if the underlying handler supports streaming. If so,
+    # Returns whether the underlying handler supports streaming. If so,
     # a streaming buffer *may* be passed when it start rendering.
     def supports_streaming?
       handler.respond_to?(:supports_streaming?) && handler.supports_streaming?