Fix refresh pattern to be customizable

[yoshi1123]

In settings.json, eclipse-jdt-ls has this config:

      "config": {
        "refresh_pattern": "\\([.a-zA-Z0-9_-]\\+\\|/\\|\\k\\+\\)$"
      },

Completion for methods/fields does not work for me with this refresh pattern. With this PR, one can change this refresh_pattern with g:lsp_settings. For example,

let g:lsp_settings = {
\ "eclipse-jdt-ls": {
\   "config": {
\     "refresh_pattern":"\\(\\k\\+\\)$"
\   }
\ }
\}