Relax development gem version

Signed-off-by: Kentaro Hayashi <hayashi@clear-code.com>

Author: kenhys

fluent-plugin-watch-objectspace.gemspec

@@ -20,9 +20,9 @@ Gem::Specification.new do |spec|
   spec.test_files    = test_files
   spec.require_paths = ["lib"]
 
-  spec.add_development_dependency "bundler", "~> 2.3.27"
-  spec.add_development_dependency "rake", "~> 13.0.6"
-  spec.add_development_dependency "test-unit", "~> 3.4.4"
-  spec.add_development_dependency "test-unit-rr", "~> 1.0.5"
+  spec.add_development_dependency "bundler", [">= 2.5.0", "< 2.6"]
+  spec.add_development_dependency "rake", "< 14"
+  spec.add_development_dependency "test-unit", "< 3.7"
+  spec.add_development_dependency "test-unit-rr", "< 1.1"
   spec.add_runtime_dependency "fluentd", [">= 0.14.10", "< 2"]
 end