Remove `-e` option in `install.sh` script

My `.bash_profile` file was as follows when installed `nvm` via `curl`.

```
-e

[[ -s /Users/okuryu/.nvm/nvm.sh ]] && . /Users/okuryu/.nvm/nvm.sh # This loads NVM
```

I guess that shell actually doesn't support -e option. So seems to unneeded these options at install.sh.