Fix UnusedVariable warning from CodeNarc.

@see http://codenarc.sourceforge.net/codenarc-rules-unused.html#UnusedVariable

No functional changes.

Author: php-coder

src/test/groovy/ru/mystamps/web/service/ImageServiceImplTest.groovy

@@ -120,7 +120,7 @@ class ImageServiceImplTest extends Specification {
 		given:
 			ImageInfoDto image = TestObjects.createImageInfoDto()
 		when:
-			String url = service.save(multipartFile)
+			service.save(multipartFile)
 		then:
 			imageDao.add(_ as String) >> image.id
 		and: