`gq -v key=value` does not accept '=' in the value.

Thank you for developing this library. I'm grateful for your work.

When I run the command `gq ${endpoint} -q {query} -v "key=YmFzZTY0IGVuY29kZWQ="`, it fails with the following error:

```
Error: cannot parse variable 'key=YmFzZTY0IGVuY29kZWQ= (multiple '=')'
```

I'm pleased that I can pass a base64-encoded value using the 'v' option.