Fix ci on Ruby 2.5

Fix an issue where the argument passing method for ERB.new in Ruby 2.5 differs from Ruby 2.6 and above, causing errors during template generation.

```
SSHKit::Runner::ExecuteError: Exception while executing as willnet@localhost: no implicit conversion of Hash into Integer
```

ref: https://ruby-doc.org/stdlib-2.5.0/libdoc/erb/rdoc/ERB.html#method-c-new

lib/capistrano/puma.rb

@@ -53,7 +53,11 @@ def compiled_template_puma(from, role)
           File.expand_path("../templates/#{from}.rb.erb", __FILE__)
       ].detect { |path| File.file?(path) }
       erb = File.read(file)
-      StringIO.new(ERB.new(erb, trim_mode: '-').result(binding))
+      if Gem::Version.new(RUBY_VERSION) < Gem::Version.new('2.6')
+        StringIO.new(ERB.new(erb, nil, '-').result(binding))
+      else
+        StringIO.new(ERB.new(erb, trim_mode: '-').result(binding))
+      end
     end
 
     def template_puma(from, to, role)