Update DefaultGenerator.java to call close()

Need to call out.close() after IOUtils.copy(in, out); when writing supporting files.

modules/swagger-codegen/src/main/java/io/swagger/codegen/DefaultGenerator.java

@@ -526,6 +526,7 @@ public class DefaultGenerator extends AbstractGenerator implements Generator {
                         if (in != null) {
                             LOGGER.info("writing file " + outputFile);
                             IOUtils.copy(in, out);
+                            out.close();
                         } else {
                             LOGGER.error("can't open " + templateFile + " for input");
                         }