[SPARK-16477] Bump master version to 2.1.0-SNAPSHOT

[rxin]

What changes were proposed in this pull request?

After SPARK-16476 (committed earlier today as #14128), we can finally bump the version number.

How was this patch tested?

N/A

[rxin]

cc @srowen

[SparkQA]

Test build #62075 has finished for PR 14130 at commit 2915bf1.

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

[srowen]

Hm I tried this recently and it failed mima. I think this has to bump the base mima version too but then it will fail because 2.0.0 isn't released. I thought we'd have to wait.

[rxin]

That's why I did #14128

Base mima version is still 1.6, and 2.0 and 2.1 currently has the same set of excludes.

[srowen]

OK, later we'd have to make the base version 2.0.0 right? that's fine though either way we have to bump something later, so was going to wait, but, no big deal either way, especially if it reduces confusion about the snapshot number

[rxin]

Yup once we actually release we can bump the base version. The good thing with the new approach is that we can now define mima excludes based on 2.0 or 2.1 versions already.

[rxin]

I'm going to merge this in master.