Support new versions of APT

Summary

Support new versions of APT

Environment

HipChat for Linux - Ubuntu 16.04 and its derivatives.

Steps to Reproduce

1. In Ubuntu 16.04
2. follow the instruction from the Website

   sudo sh -c 'echo "deb https://atlassian.artifactoryonline.com/atlassian/hipchat-apt-client $(lsb_release -c -s) main" > /etc/apt/sources.list.d/atlassian-hipchat4.list'
   wget -O - https://atlassian.artifactoryonline.com/atlassian/api/gpg/key/public | sudo apt-key add -
   sudo apt-get update
   sudo apt-get install hipchat4

Expected Results

Installation is successful

Actual Results

W: Failed to fetch https://atlassian.artifactoryonline.com/atlassian/hipchat-apt-client/dists/xenial/Release No Hash entry in Release file /var/lib/apt/lists/partial/atlassian.artifactoryonline.com_atlassian_hipchat-apt-client_dists_xenial_Release, which is considered strong enough for security purposes
E: Some index files failed to download. They have been ignored, or old ones used instead.

Notes

New versions of APT require to include "Hash:" field in release file. Also SHA1 hashes are now deprecated and APT tosses a warning about that. So there should be SHA256 hashes added.

Here's an exact error message shown after "apt-get update" command:
W: Failed to fetch https://atlassian.artifactoryonline.com/atlassian/hipchat-apt-client/dists/xenial/Release No Hash entry in Release file /var/lib/apt/lists/partial/atlassian.artifactoryonline.com_atlassian_hipchat-apt-client_dists_xenial_Release, which is considered strong enough for security purposes
E: Some index files failed to download. They have been ignored, or old ones used instead.

Workaround

Download and install .deb file directly here