Install script does not support Apple Silicon

Hi,

I'm new to nvim/vim and I'm attempting to create a setup which allows me to move away from VSCode, so I'm very happy to see this plugin!

However, I get the following error when launching `nvim` after installing this plugin and it's dependencies:

```
TabNine: exit 2
```

I'm on a M1 Mac mini, if that's of consequence.

Thanks!