Avoid double tap feature in insert-mode (#558)

Author: hrsh7th

autoload/lsp/ui/vim/output.vim

@@ -292,6 +292,7 @@ function! lsp#ui#vim#output#preview(server, data, options) abort
        \ && type(g:lsp_preview_doubletap) == 3
        \ && len(g:lsp_preview_doubletap) >= 1
        \ && type(g:lsp_preview_doubletap[0]) == 2
+       \ && mode()[0] !=# 'i'
         echo ''
         return call(g:lsp_preview_doubletap[0], [])
     endif