md preview: fix the node package installation.

- Fixes the markdown preview node package installation.
- Removes the theme configuration.

Co-Authored-by: iGor milhit <igor.milhit@unige.ch>

lua/custom/plugins/markdownpreview.lua

@@ -1,9 +1,6 @@
 -- makdown-preview.nvim
 -- installed with code found at https://github.com/iamcco/markdown-preview.nvim/issues/558#issuecomment-1514701537
 
--- Force the light theme, no matter the system option is.
-vim.cmd([[ let g:mkdp_theme = 'light' ]])
-
 return {
   {
     "iamcco/markdown-preview.nvim",
@@ -12,6 +9,6 @@ return {
       'markdown'
     },
     lazy = true,
-    build = "cd app && yarn install",
+    build = "cd app && npm install && git reset --hard",
   },
 }