Warning: connect.static is not a function Use –force to continue

You have to install connect and serve-static:

npm install --save-dev grunt-contrib-connect serve-static 

And then you have to import serve-static in Gruntfile.js:

module.exports = function (grunt) {
  ...
  var serveStatic = require('serve-static');

  grunt.initConfig({
  ...
    connect: {
    ...
      livereload: {
        options: {
          middleware: function(connect) {
            return [
              serveStatic('.tmp'),
              connect().use('/bower_components', serveStatic('./bower_components')),
              serveStatic(config.app)
            ];
          }
        }
      }