community/pamixer: upgrade to 1.6

There are two important changes:

• Added the state column for the options --list-sources and --list-sinks (https://github.com/cdemoulins/pamixer/issues/45). I need this for the avizo package.
• Replaced Boost.Program_options with a much lighter dependency (https://github.com/cdemoulins/pamixer/issues/46).

I've asked to release a new version in https://github.com/cdemoulins/pamixer/issues/51 and a month ago in #45. (EDIT: 1.6 is released)