chore: depend on 'logger' explicitly (#612)

This used to be shipped with Ruby, as a bundled gem, but is now a regular gem.
Ruby 3.5.0 no longer includes this gem by default.

Depending on it avoids a warning being emitted.

honeybadger.gemspec

@@ -34,4 +34,6 @@ Gem::Specification.new do |s|
   s.require_paths = ['lib', 'vendor/capistrano-honeybadger/lib']
 
   s.executables << 'honeybadger'
+
+  s.add_dependency 'logger'
 end