fixed scala errors

Author: Daniel Borowski

language/scala/scala.go

@@ -10,7 +10,8 @@ func Run(files []string, stdin string) (string, string, error) {
 
 	args := append([]string{"scalac"}, files...)
 	stdout, stderr, err := cmd.Run(workDir, args...)
-	if err != nil {
+	
+	if err != nil || stderr != "" {
 		return stdout, stderr, err
 	}