Fix issue with 2.6.

  1) Listen::Adapter::Linux _callback recognizes close_write as modify
     Failure/Error: rel_path = path.relative_path_from(dir).to_s

     TypeError:
       no implicit conversion of RSpec::Mocks::InstanceVerifyingDouble into String
     # ./lib/listen/adapter/linux.rb:48:in `_process_event'
     # ./lib/listen/adapter/base.rb:42:in `block (2 levels) in configure'
     # ./spec/lib/listen/adapter/linux_spec.rb:99:in `block (5 levels) in <top (required)>'
     # ./spec/lib/listen/adapter/linux_spec.rb:98:in `each'
     # ./spec/lib/listen/adapter/linux_spec.rb:98:in `block (4 levels) in <top (required)>'
     # ./spec/lib/listen/adapter/linux_spec.rb:113:in `block (3 levels) in <top (required)>'

lib/listen/adapter/linux.rb

@@ -45,7 +45,7 @@ def _process_event(dir, event)
         # will need to have a custom recursion implemented
         # to properly match events to configured directories
         path = Pathname.new(event.watcher.path) + event.name
-        rel_path = path.relative_path_from(dir).to_s
+        rel_path = path.relative_path_from(dir.to_s).to_s
 
         _log(:debug) { "inotify: #{rel_path} (#{event.flags.inspect})" }