Fix ruby 2.7 keyword arguments deprecation

Similar to https://github.com/grpc/grpc/pull/22915

src/ruby/lib/grpc/generic/interceptors.rb

@@ -172,7 +172,7 @@ module GRPC
       i = @interceptors.pop
       return yield unless i
 
-      i.send(type, args) do
+      i.send(type, **args) do
         if @interceptors.any?
           intercept!(type, args) do
             yield