build: Declare grunt-cli dependency

build: Declare grunt-cli dependency

A long time ago, npm did not support using command line programs
within 'npm test' (not unless harcoding a path to node_modules/bin/...
within packages.json/scripts/test). But this has been long supported.

Declaring a (dev)dependency will provide its binaries to the
PATH used by the subshell 'npm test' creates internally.

Add grunt-cli so that developers don't have to manually install it.

Change-Id: I6a7fafa3c6e40d2407f07c514167ab9fc7661685