[SPARK-13506][MLLIB] Fix the wrong parameter in R code comment in AssociationRulesSuite

JIRA: https://issues.apache.org/jira/browse/SPARK-13506

## What changes were proposed in this pull request?

just chang R Snippet Comment in  AssociationRulesSuite

## How was this patch tested?

unit test passsed

Author: Zheng RuiFeng <ruifengz@foxmail.com>

Closes #11387 from zhengruifeng/ars.