Missing #!/usr/bin/env bash in main bash script

The bash script that gets downloaded to `~/.sourcerer/sourcerer` is missing the `#!/usr/bin/env bash` header.

So when I run `sourcerer` in my terminal I get the following error message:
```
Failed to execute process '/usr/local/bin/sourcerer'. Reason:
exec: Exec format error
The file '/usr/local/bin/sourcerer' is marked as an executable but could not be run by the operating system.
```