remove the space from the importer artifact name (rebased onto develop)



This is the same as gh-1331 but rebased onto develop.

----

Previously after the `release-clients` target I was getting,
```
$ ls target/*-mac.zip
target/OMERO.editor-4.4.8-DEV-ice33-mac.zip
target/OMERO.importer -4.4.8-DEV-ice33-mac.zip
target/OMERO.insight-4.4.8-DEV-ice33-mac.zip
```