fix(pkg/downloader): Use system generated temp directory

Signed-off-by: Josh Soref <jsoref@users.noreply.github.com>

pkg/downloader/manager.go

@@ -247,7 +247,11 @@ func (m *Manager) downloadAll(deps []*chart.Dependency) error {
 	}
 
 	destPath := filepath.Join(m.ChartPath, "charts")
-	tmpPath := filepath.Join(m.ChartPath, "tmpcharts")
+	tmpPath, err := ioutil.TempDir("", "tmpcharts-*")
+	if err != nil {
+		return errors.Wrap(err, "failed to create tmpcharts dir")
+	}
+	os.Remove(tmpPath)
 
 	// Create 'charts' directory if it doesn't already exist.
 	if fi, err := os.Stat(destPath); err != nil {