cjson missing during installation

[githubgnulinux]

:45 | script: downloading list of scripts...
:45 | Plugins loaded: alias, aspell, charset, exec, fifo, guile, irc,
| javascript, logger, lua, perl, python, relay, ruby, script, tcl,
| trigger, xfer
:47 | script: 362 scripts for WeeChat 1.6
:22 | lua: loading script ".../.weechat/lua/autoload/matrix.lua"
:22 =!= | lua: unable to execute file
| ".../.weechat/lua/autoload/matrix.lua"
:22 =!= | lua: error: .../.weechat/lua/autoload/matrix.lua:48: module
| 'cjson' not found:
:22 | no field package.preload['cjson']
:22 | no file './cjson.lua'
:22 | no file '/usr/local/share/lua/5.1/cjson.lua'
:22 | no file '/usr/local/share/lua/5.1/cjson/init.lua'
:22 | no file '/usr/local/lib/lua/5.1/cjson.lua'
:22 | no file '/usr/local/lib/lua/5.1/cjson/init.lua'
:22 | no file '/usr/share/lua/5.1/cjson.lua'
:22 | no file '/usr/share/lua/5.1/cjson/init.lua'
:22 | no file './cjson.so'
:22 | no file '/usr/local/lib/lua/5.1/cjson.so'
:22 | no file '/usr/lib/x86_64-linux-gnu/lua/5.1/cjson.so'
:22 | no file '/usr/lib/lua/5.1/cjson.so'
:22 | no file '/usr/local/lib/lua/5.1/loadall.so'