Update capistrano requirement from >= 3.7.0, < 3.20.0 to >= 3.7.0, < 3.21.0

Updates the requirements on [capistrano](https://github.com/capistrano/capistrano) to permit the latest version.
- [Release notes](https://github.com/capistrano/capistrano/releases)
- [Commits](capistrano/capistrano@v3.7.0...v3.20.0)

---
updated-dependencies:
- dependency-name: capistrano
  dependency-version: 3.20.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

capistrano-scm-git_with_submodule_and_resolv_symlinks.gemspec

@@ -19,7 +19,7 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
 
-  spec.add_dependency "capistrano", ">= 3.7.0", "< 3.20.0"
+  spec.add_dependency "capistrano", ">= 3.7.0", "< 3.21.0"
   spec.add_development_dependency "bundler"
   spec.add_development_dependency "rake"
   spec.add_development_dependency "rspec", "~> 3.0"