DDC-3726: [GH-1401] Remove HHVM-nightly builds

[doctrinebot]

Jira issue originally created by user @doctrinebot:

This issue is created automatically through a Github pull request on behalf of stof:

Url: #1401

Message:

hhvm-nightly is not available anymore on Travis because HHVM dropped support for Ubuntu Precise, which is still used by Travis.

This avoids creating useless jobs in the matrix which are killed by Travis from the start.

[doctrinebot]

• is referenced by DBAL-1226: [GH-853] Remove HHVM-nightly builds

[doctrinebot]

Comment created by @doctrinebot:

A related Github Pull-Request [GH-1401] was assigned:
#1401

[doctrinebot]

Comment created by @doctrinebot:

A related Github Pull-Request [GH-1401] was labeled:
#1401

[doctrinebot]

Comment created by @doctrinebot:

A related Github Pull-Request [GH-1401] was merged:
#1401

[doctrinebot]

Issue was closed with resolution "Fixed"