Allow running bundler v2.x

Author: valscion

protobuf_nested_struct.gemspec

@@ -27,7 +27,7 @@ Gem::Specification.new do |spec|
   spec.require_paths = ["lib"]
   spec.add_dependency "google-protobuf"
 
-  spec.add_development_dependency "bundler", "~> 1.16"
+  spec.add_development_dependency "bundler"
   spec.add_development_dependency "rake", "~> 10.0"
   spec.add_development_dependency "rspec", "~> 3.0"
   spec.add_development_dependency "pry"