(GH-311) Explicitly require Facter

Changes with how Puppet includes Facter as suggested in the ticket means that we need to explicitly include the library.

Author: da-ar

lib/puppet_languageserver.rb

@@ -72,6 +72,7 @@ def self.require_gems(options)
     begin
       require 'lsp/lsp'
       require 'puppet'
+      require 'facter'
     rescue LoadError => e
       log_message(:error, "Error while loading a critical gem: #{e} #{e.backtrace}")
       return