Fix lint warning & add Go 1.9 to the mix

.travis.yml

@@ -6,6 +6,7 @@ language: go
 go:
   - 1.7.x
   - 1.8.x
+  - 1.9.x
   - master
 
 go_import_path: github.com/smira/aptly

deb/list.go

@@ -518,7 +518,7 @@ func (l *PackageList) FilterWithProgress(queries []PackageQuery, withDependencie
 				}
 
 				searchResults := l.Search(dep, true)
-				if searchResults != nil {
+				if len(searchResults) > 0 {
 					for _, p := range searchResults {
 						if dependencyOptions&DepVerboseResolve == DepVerboseResolve && progress != nil {
 							progress.ColoredPrintf("@{g}Injecting package@|: %s", p)