Update version to 1.3.7

We have agreed to keep all PEcAn module versions in sync, e.g. all of the outputs from the following command should currently be at 1.3.7:

This required:

```sh
git checkout -b update_version
sed -i 's/1.3.3/1.3.7/g' scripts/updateDescription.sh
./scripts/updateDescription.sh
git push origin update_version
```

... not sure if there is a way to automate this. Its not difficult, but should be part of the version release.

And ... not sure if we want to add this to the 1.3.7 tag.