[MINOR][R] Fix R lint failure

[HyukjinKwon]

What changes were proposed in this pull request?

The lint failure bugged me:

R/SQLContext.R:715:97: style: Trailing whitespace is superfluous.
#'        file-based streaming data source. \code{timeZone} to indicate a timezone to be used to
                                                                                                ^
tests/fulltests/test_streaming.R:239:45: style: Commas should always have a space after.
  expect_equal(times[order(times$eventTime),][1, 2], 2)
                                            ^
lintr checks failed.

and I actually saw https://amplab.cs.berkeley.edu/jenkins/job/spark-master-test-sbt-hadoop-2.6-ubuntu-test/500/console too. If I understood correctly, there is a try about moving to Unbuntu one.

How was this patch tested?

Manually tested by ./dev/lint-r:

...
lintr checks passed.

[HyukjinKwon]

cc @felixcheung and @shaneknapp

[SparkQA]

Test build #88519 has finished for PR 20879 at commit bdd024b.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[shaneknapp]

i've had to punt on figuring out how to get spark to reliably build across branches on the ubuntu workers... mostly because i haven't been able to successfully get the proper versions of various R packages installed that mirror what's on the old and barely touched centos workers.

[shaneknapp]

other than that, this PR LGTM++

[felixcheung]

thanks! those are on me then.
are we not running lintr? or these checks are on the newer version only?

[HyukjinKwon]

Yup, we are running old lint in PR builders and those are on the newer one.

[HyukjinKwon]

Merged to master and branch-2.3.

Thanks for reviewing this @shaneknapp and @felixcheung.