Startify adds ~100ms to VimEnter autocommand

Startify seems to add 100ms or so to VimEnter autocommand. When using dstein64/vim-startuptime to profile startuptime

```
event time percent
VimEnter autocommand 109.76 27.92
```

If I comment out "set filetype=startify" on line 161 of autoload/startify.vim VimEnter autocommand returns to normal duration

```
event time percent
VimEnter autocommand 12.08 4.76
```

Is this expected or can it be improved?

Reproduce the startup profile with dstein64/vim-startuptime, then inspect autoload/startify.vim around line 161, where `set filetype=startify` is enabled during VimEnter. Compare the VimEnter timings with and without that setting; done means determining whether the delay is expected and documenting or improving the measured behavior.

Written by the indexing model from the issue text.