feat(resize): add ability to grow and shrink the tree when drawing (#1293)

Will adapt the view size based on the longest line.
fixes #865

README.md

@@ -83,6 +83,7 @@ require'nvim-tree'.setup { -- BEGIN_DEFAULT_OPTS
   reload_on_bufenter = false,
   respect_buf_cwd = false,
   view = {
+    adaptive_size = false,
     width = 30,
     height = 30,
     hide_root_folder = false,