grunt-riotts-precompile uses a deprecated grunt version.

[anacierdem]

npm install grunt-riotts-precompile --save-dev

results in;

npm WARN peerDependencies The peer dependency grunt@~0.4.5 included from grunt-riotts-precompile will no
npm WARN peerDependencies longer be automatically installed to fulfill the peerDependency
npm WARN peerDependencies in npm 3+. Your application will need to depend on it explicitly.

...

npm ERR! Darwin 15.6.0
npm ERR! argv "/usr/local/bin/node" "/usr/local/bin/npm" "install" "grunt-riotts-precompile" "--save-dev"
npm ERR! node v4.6.1
npm ERR! npm  v2.15.9
npm ERR! code EPEERINVALID

npm ERR! peerinvalid The package [email protected] does not satisfy its siblings' peerDependencies requirements!
npm ERR! peerinvalid Peer [email protected] wants grunt@~0.4.5

npm ERR! Please include the following file with any support request:
npm ERR!     ***

Manually installing grunt 0.4.5 resolves this issue, which is an outdated version.