@spoqa → @nirum-lang: Update links and reconnect services

[dahlia]

Although we've transferred the Git repository from @spoqa to @nirum-lang, other connected services and links to the repository from other web pages should be updated as well.

• Gitter
• Travis CI
• AppVeyor CI
• Internal documents
• External documents

Anymore?

[dahlia]

I've emailed a transfer request to Gitter's customer service.

[dahlia]

Still no response nor action from Gitter's C/S…