fix(rockspec) missing 'const.lua'

[xHasKx]

Adding new files to rockspec file can be postponed until new version release (version bump) because luarocks uses git tag to find proper commit to install lib. Anyway thanks, I'll merge it before the next release.

[Tieske]

as a suggestion; can you add an SCM rockspec, and move the actual versioned one in a subdirectory?

that will allow the use of the SCM one to quickly build and install from the repo. Also during development, the SCM one can be updated, and upon release the SCM one is copied into a versioned one.

luarocks install luamqtt --dev would install the latest master version based on the SCM one, if you upload that one to LuaRocks as well.

Examples are here:

• scm rockspec: https://github.com/lunarmodules/copas/blob/master/copas-cvs-6.rockspec
• rockspec dir: https://github.com/lunarmodules/copas/tree/master/rockspec

I can provide a new (or update this) PR if you want.

[Tieske]

added a commit to implement the suggested SCM rockspec.