Use "io.github" prefix for RDNN

[ryonakano]

Fixes #158 Replaced with: $ git grep -l com.github | xargs sed -i "s/com\(.\)github/io\1github/g"

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We should not use the "com.github" prefix because we don't have any control over the "github.com" domain.

See also:

• https://docs.flatpak.org/en/latest/conventions.html
• https://docs.flathub.org/docs/for-app-authors/requirements