Fix argument passing (#186)

Concatenating the command line option and its value doesn't really work.
The shell treats `--opt val` as a single argument `--opt val` instead of
`--opt` `val` and fails to execute. This PR fixes that by separating
options from their values.

Error example:
```
error: unexpected argument '--workers-path ~/.cargo/bin/workers-1.6' found

  tip: a similar argument exists: '--workers-path'
```

Co-authored-by: Javier Viola <[email protected]>