Why doesn't GULP refresh the page on a change in a file?

Question

gulp.js

I follow the changes in the style file, when the file changes, I want the task to be executed and the page to be reloaded, the task is executed but the page is not reloaded

, this is the task itself:
gulp.task('libs_styles', () => {
return gulp
.src('src/ scss/vendor.scss')
.pipe(map.init())
.pipe(sass({
outputStyle: 'compressed'
}).on('error', sass.logError))
.pipe(concat('vendor.min .css'))
.pipe(map.write('../sourcemaps/'))
.pipe(size(settings_size))
.pipe(gulp.dest('build/css/'))

});

This is how I watch the file:
gulp.watch('src/scss/vendor.scss',