Gemfile in instana-1.9.0 vs Gemfile in instana-1.9.1

@@ -8,10 +8,10 @@
   gem 'webmock'
   gem 'puma'
 
   # Rack v2 dropped support for Ruby 2.2 and higher.
   if RUBY_VERSION < '2.2'
-    gem 'rack', '< 2.0'
+    gem 'rack', '~> 1.6'
   end
   gem 'rack-test'
 
   # public_suffix dropped support for Ruby 2.1 and earlier.
   gem 'public_suffix', '< 3.0'