Empty version file in GCS

[robwhitby]

We use semver-resource with GCS and occasionally get these errors:

error bumping version: parsing number in bucket: Version string empty

error checking for new versions: parsing number in bucket: Version string empty

There is no error from the last put which bumped the version, but the file in GCS is indeed empty.

To fix it we have to manually write the latest version with gsutil.

# careful not to add newline
echo -n '1.2.3' > /tmp/v
gsutil cp /tmp/v gs://some-path