remove the space from the importer artifact name

Previously after release-clients 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
Merge pull request #1331 from mtbc/fix-importer-artifact-name

remove the space from the importer artifact name