fix code snippet in PERFORMANCE section (#866)
fix code snippet in PERFORMANCE section (#866)

The variable name was different from the implementation
https://github.com/prabirshrestha/vim-lsp/blob/11b13507002e42adf77b35ed63b4164ecc5d5b8a/plugin/lsp.vim#L6
prabirshrestha/vim-lsp,prabirshrestha/vim-lsp