Promoted Versions should not include unstable versions

[dualspiral]

Describe the bug Plugin versions that are marked as "unstable" should not be included in the promoted versions section.

To Reproduce

• Ensure you have a "stable" version of your plugin for a specific Sponge API
• Upload a new plugin, mark as unstable.
• Look at the promoted versions

Expected behavior

• The unstable version should not be promoted, the list should remain untouched.

Screenshots N/A

Environment

• macOS / Firefox 71.0b8

Additional context Look at version 2.0.0-ALPHA-1-S7.1 for Nucleus (https://ore.spongepowered.org/Nucleus/Nucleus/)