bump up 1.x branch to 1.7.0

[szha]

Description

bump up 1.x branch to 1.7

Checklist

Essentials

Please feel free to remove inapplicable items for your PR.

• Changes are complete (i.e. I finished coding on this PR)
• To the best of my knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change

Changes

• bump up 1.x branch to 1.7

Comments

• See [RFC] New Branches for MXNet 1.x, 1.7.x, and 2.x #17701 for branch use.
• See [Discussion] 1.7.0 Roadmap #16864 for scope

[gigasquid]

Thanks for getting the PR together. I think one Clojure file got left out by accident. The main project.clj file https://github.com/apache/incubator-mxnet/blob/master/contrib/clojure-package/project.clj#L18

Do you mind adding? Or I can make a PR to your branch if you prefer.

[leezu]

@szha Seems this was merged to the wrong branch and broke nightly tests

[2020-03-03T19:53:00.983Z] [ERROR] Failed to execute goal on project mxnet-scala-demo: Could not resolve dependencies for project Demo:mxnet-scala-demo:pom:1.0-SNAPSHOT: Failed to collect dependencies at org.apache.mxnet:mxnet-full_2.11-linux-x86_64-cpu:jar:[1.7.0-SNAPSHOT,): No versions available for org.apache.mxnet:mxnet-full_2.11-linux-x86_64-cpu:jar:[1.7.0-SNAPSHOT,) within specified range -> [Help 1]

[szha]

@leezu I realized it afterwards and cherry-picked the change to 1.x. I think the problem here is that there's no new scala mxnet released yet. @lanking520 could you look into the status for the build?