fix: integrate review commentsé

Author: Gu1nness

pbm/storage/fs/fs.go

@@ -65,7 +65,7 @@ func (cfg *Config) IsSameStorage(other *Config) bool {
 
 func (cfg *Config) Cast() error {
 	if cfg == nil {
-		return errors.New("Missing blackhole configuration with blackhole storage type.")
+		return errors.New("missing filesystem configuration with filesystem storage type.")
 	}
 	if cfg.Path == "" {
 		return errors.New("path can't be empty")

pbm/storage/s3/s3.go

@@ -201,7 +201,7 @@ func (cfg *Config) IsSameStorage(other *Config) bool {
 
 func (cfg *Config) Cast() error {
 	if cfg == nil {
-		return errors.New("Missing S3 configuration with S3 storage type.")
+		return errors.New("missing S3 configuration with S3 storage type")
 	}
 	if cfg.Region == "" {
 		cfg.Region = defaultS3Region