fix diagnostic cfg path error (#173)

* fix diagnostic cfg path error

* add defult lsp.diagnostic setting

* Update navigator.lua

Simplify logic

Co-authored-by: rayx <rayx.cn@gmail.com>

lua/navigator.lua

@@ -229,7 +229,8 @@ M.setup = function(cfg)
   require('navigator.hierarchy')
   require('navigator.implementation')
 
-  require('navigator.diagnostics').config(cfg.diagnostic)
+  cfg.lsp = cfg.lsp or _NgConfigValues.lsp
+  require('navigator.diagnostics').config(cfg.lsp.diagnostic)
   if not _NgConfigValues.loaded then
     _NgConfigValues.loaded = true
   end