Fix copy pasta

Author: garydgregory

src/main/java/org/apache/commons/csv/CSVFormat.java

@@ -579,7 +579,7 @@ public Builder setHeaderComments(final Object... headerComments) {
          * </p>
          * <pre>
          * builder.setCommentMarker('#')
-         *        .setHeaderComments("Generated by Apache Commons CSV", Instant.ofEpochMilli(0));
+         *        .setHeaderComments("Generated by Apache Commons CSV", Instant.ofEpochMilli(0).toString());
          * </pre>
          * <p>
          * writes: