ERROR No such variable: nextflow

When I run the current version of the pipeline, I get this:
```
N E X T F L O W  ~  version 0.22.2
Launching `main.nf` [naughty_sinoussi] - revision: 62c3b2711f
ERROR ~ No such variable: nextflow
```
Somewhat ironically, it is the version check that causes this:
```
if (!nextflow.version.matches('>= 0.25.0')) exit 1, "Nextflow version 0.25.0 or greater is needed to run this workflow"
```
