Updates the gemspec to treat the route_guide client and server as binaries

ruby/grpc-demo.gemspec

@@ -11,7 +11,7 @@ Gem::Specification.new do |s|
   s.description   = 'Simple demo of using gRPC from Ruby'
 
   s.files         = `git ls-files -- ruby/*`.split("\n")
-  s.executables   = `git ls-files -- ruby/*client.rb ruby/*server.rb`.split("\n").map do |f|
+  s.executables   = `git ls-files -- ruby/greeter*.rb ruby/route_guide/*.rb`.split("\n").map do |f|
     File.basename(f)
   end
   s.require_paths = ['lib']