Fix broken gradle repo URL

[steventrouble]

/gradle/ doesn't work anymore, but /artifactory/ works.

The PR is in accordance with the Developer's Certificate of Origin.

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Tested: ./gradlew build in several subdirs.

Before:

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':node-driver:compileKotlin'.
> Could not resolve all files for configuration ':node-driver:compileClasspath'.
   > Could not find org.gradle:gradle-tooling-api:5.6.4.

After: No errors