[MINOR][DOC] Remove spaces following slashs

[dongjoon-hyun]

What changes were proposed in this pull request?

This PR merges multiple lines enumerating items in order to remove the redundant spaces following slashes in Structured Streaming Programming Guide in 2.0.2-rc1.

• Before: Scala/ Java/ Python
• After: Scala/Java/Python

How was this patch tested?

Manual by the followings because this is documentation update.

cd docs
SKIP_API=1 jekyll build

[SparkQA]

Test build #67782 has finished for PR 15686 at commit b385a4c.

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

[dongjoon-hyun]

Thank you for review and approval, @srowen !

[HyukjinKwon]

Build started: [SparkR] ALL
Diff: master...spark-test:1D4EC6E8-F2CF-4585-9745-0AE5956F211C

:)

[rxin]

@HyukjinKwon why are the appveyor checks failing?

[HyukjinKwon]

@rxin, it seems spurious. The message seems meaning the failure when the commit is virtually not mergeable[1].

It seems it fails time to time for various reasons. For example, in some cases, it seems failing to clone due to network problem within AppVeyor[2].

it is able to re-trigger via Web UI but it seems committers are also not allowed to access to it. Due to this problem, I temporarily made a bunch of scripts[3] to manually launch another build via @spark-test account. I can run the build and leave the comment above until we find a better way to handle it. (treat me like a bot)

[1]http://help.appveyor.com/discussions/problems/4912-merge-commit-does-not-start-build-in-the-repo-i-make-pull-request-for
[2]https://ci.appveyor.com/project/ApacheSoftwareFoundation/spark/build/256-master
[3]https://github.com/HyukjinKwon/spark-appveyor

[HyukjinKwon]

I believe the message indicates the same case with the PR 15673 and 15689 but it seems spurious in this case.

[srowen]

This change seems fine.

If Appveyor is encountering errors regularly, we might consider disabling it, just because it wouldn't be giving useful information if most failures were spurious.

[HyukjinKwon]

There are three problems with it.

• it starts the build when someone merges the latest upstream (not rebases) when pushing more commits in its PR (as the merged one usually has the changes in R) - this case seems fine though because usually it succeeds to build. Also actually I asked this case to AppVeyor but I haven't received the reply.
• it sometimes fails to build (it is relatively rare I believe).
• it leaves a failure mark on other branches when someone opens a PR from a branch to another branch.

I am neutral because it seems the cases are not often. I may open a JIRA if I incline toward disabling this or please feel free to create a JIRA if anyone feels so. (Let me please cc @shivaram. I would like him to know about this).

[shivaram]

Yeah I think it'll be a good idea to know the error rate we hit. @HyukjinKwon It might also be good to create an INFRA ticket to see if we can re-trigger the AppVeyor builds somehow ?

[HyukjinKwon]

@dongjoon-hyun I am sorry for unrelated comments here. All these comments are not related with this PR.

@shivaram Sure, Let me try to create a JIRA. I will cc you. We might be able to talk more there.

[dongjoon-hyun]

Never mind, @hyunjinkwon .
I was also curious about AppVoyer failure. :)

[srowen]

Merged to master

[dongjoon-hyun]

Thank you for merging, @srowen .