Why gulp does not automatically refresh js?

Good day!

Tell me, why Gulp of coffee only updates at the start, in the process, when files coffee nothing happens.

gulpfile.js:

var gulp = require('gulp'),
 jade = require('gulp-jade'),
 stylus = require('gulp-stylus'),
 coffee = require('gulp-coffee'),
 livereload = require('gulp-livereload'),
 imagemin = require('gulp-imagemin'),
 concat = require('gulp-concat'),
 connect = require('connect'),
 serveStatic = require('serve-static'),
 nib = require('nib');


/*
 * Create tasks 
*
 * stylus for the CSS preprocessor Stylus
 * jade – to-HTML preprocessor Jade
 * coffee – JavaScript-preprocessor CoffeеScript
 * concat – stick all the CSS and JS in separate files
*/

gulp.task('stylus', function() {
gulp.src('./styl/*.styl')
 .pipe(stylus({use: nib(), compress: true}))
 .on('error', console.log) // Print errors to the console
 .pipe(gulp.dest('./public/css/')) // Print the generated CSS files in the same folder with the same name but with different extension
 .pipe(livereload()); // Restart the server LiveReload
});

gulp.task('jade', function(){
gulp.src('./*.jade')
 .pipe(jade({pretty: true}))
 .on('error', console.log) // Print errors to the console
 .pipe(gulp.dest('./public/')) // Print the generated HTML files in the same folder with the same name but with different extension
 .pipe(livereload()); // Restart the server LiveReload
});

gulp.task('coffee',function(){
gulp.src('./coffee/*.coffee')
 .pipe(coffee({bare: true}))
 .on('error', console.log) // Print errors to the console
 .pipe(gulp.dest('./public/js')) // Print the generated JavaScript files in the same folder with the same name but with different extension
 .pipe(livereload()); // Restart the server LiveReload
});

gulp.task('concat', function(){
gulp.task('coffee');
gulp.src('./public/js/*.js')
.pipe(concat('scripts.js'))
.pipe(gulp.dest('./public/min/'))
.pipe(livereload());
gulp.task('styl');
gulp.src('./public/css/*.css')
.pipe(concat('styles.css'))
.pipe(gulp.dest('./public/min/'))
.pipe(livereload());
});

gulp.task('imagemin',function(){
gulp.src('./img/**/*')
.pipe(imagemin())
.pipe(gulp.dest('./public/img/'));
});

/*
 * Create a web server to work with the project via the browser
*/
 gulp.task('server', function() {
connect()
.use(require('connect-livereload')())
 .use(serveStatic(__dirname + '/public'))
.listen('3333');

 console.log('Server running at http://localhost:3333');
});

/*
 * Create a task, looking for changes
*/
 gulp.task('watch', function(){
livereload.listen();
gulp.watch('./styl/*.styl',['stylus']);
gulp.watch('./*.jade',['jade']);
gulp.watch('./coffee/*.coffee',['coffee']);
gulp.watch(['./public/js/*.js','./public/css/*.css'],['concat']);
gulp.watch('./img/**/*',['imagemin']);
gulp.start('server');
});

 gulp.task('default',['watch','stylus','jade','coffee','concat','imagemin']);