Broken dependencies for BitMask

Trying to install BitMask on Trisquel 6 so I can try out the new RiseUp Black services:
https://dl.bitmask.net/linux/

Repo seemed to add ok, but when I tried to install the package, terminal responded with a long list of broken dependencies:

root@BISHOP:~# apt-get install bitmask leap-keyring
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
bitmask : Depends: python-zmq (>= 14.4.1-1.1) but it is not going to be installed
Depends: python (>= 2.7.5-5~) but 2.7.3-0ubuntu2.2 is to be installed
Depends: soledad-client (>= 0.6.0) but it is not going to be installed
Depends: leap-keymanager but it is not going to be installed
Depends: leap-mail (>= 0.3.11) but it is not going to be installed
Depends: python-leap-common (>= 0.3.7) but it is not going to be installed
Depends: python-requests (>= 1.2.3-1) but it is not going to be installed
Depends: python-jsonschema (>= 0.7.0) but it is not installable
E: Unable to correct problems, you have held broken packages.

Suggestions?