Add Opera Neon, first release

[bvankuik]

If there’s a checkbox you can’t complete for any reason, that's okay, just explain in detail why you weren’t able to do so.

After making all changes to the cask:

• brew cask audit --download {{cask_file}} is error-free.
• brew cask style --fix {{cask_file}} reports no offenses.
• The commit message includes the cask’s name and version. Caveat: Opera Neon doesn't seem to be versioned explicitly, so in the commit version, I just noted "first release"

Additionally, if adding a new cask:

• Named the cask according to the token reference.
• brew cask install {{cask_file}} worked successfully.
• brew cask uninstall {{cask_file}} worked successfully.
• Checked there are no open pull requests for the same cask.
• Checked that the cask was not already refused in closed issues.

[miccal]

Please submit this to caskroom/homebrew-versions.

[miccal]

Homebrew/homebrew-cask-versions#3129.