Auto merge of #169 - premist:update-puma, r=olleolleolle

Update Puma dependency to ~> 3.10

Tried to install Puma on freshly installed Arch Linux instance failed since older version of Puma doesn't support latest OpenSSL version([related issue](puma/puma#1380)).

This PR updates Puma dependency to the latest available version, 3.10. Newer version of Puma introduced some changes to Puma::CLI interface, so I also updated integration test to reflect it.

gemstash.gemspec

@@ -33,7 +33,7 @@ you push your own private gems as well."
   spec.add_runtime_dependency "faraday", "~> 0.9"
   spec.add_runtime_dependency "faraday_middleware", "~> 0.10"
   spec.add_runtime_dependency "lru_redux", "~> 1.1"
-  spec.add_runtime_dependency "puma", "~> 2.14"
+  spec.add_runtime_dependency "puma", "~> 3.10"
   spec.add_runtime_dependency "server_health_check-rack", "~> 0.1"
   spec.add_runtime_dependency "sequel", "~> 4.26"
   spec.add_runtime_dependency "sinatra", "~> 1.4"

spec/support/test_gemstash_server.rb

@@ -53,7 +53,7 @@ def start
   def stop
     return if @stopped
     @stopped = true
-    @puma_cli.halt
+    @puma_cli.launcher.stop
   end
 
   def join