Suggestion: secure way of loading colorscheme

If by any change packer fails on installing the colorscheme the starting process will not fail or bother the user more than needed:

```lua
-- in my config I use ayu colorscheme
local colorscheme = "ayu-dark"
local status_ok, _ = pcall(vim.cmd, "colorscheme " .. colorscheme)
if not status_ok then
    vim.notify("colorscheme " .. colorscheme .. " not found!")
    return
end
```