gulpfile.js

var gulp = require('gulp');
var sass = require('gulp-sass');
var prefix = require('gulp-autoprefixer');
var browserSync = require('browser-sync');
var reload = browserSync.reload;
var nodemon = require('gulp-nodemon');

gulp.task('sass', function () {
    return gulp.src('scss/*.scss')
        .pipe(sass({outputStyle: 'compressed'}, {errLogToConsole: true}))
        .pipe(prefix("last 2 versions", "> 1%", "ie 8", "Android 2", "Firefox ESR"))
        .pipe(gulp.dest('css'))
        .pipe(reload({stream:true}));
});

gulp.task('browser-sync', ['nodemon'], function() {
    browserSync.init(null, {
        proxy: "localhost:8080"
    });
});

gulp.task('default', ['sass', 'browser-sync'], function () {
    gulp.watch("scss/*.scss", ['sass']);
    gulp.watch(["public/js/**/*.js", "public/*.html"], reload);
});

gulp.task('nodemon', function (cb) {
    return nodemon({script: 'app.js'}).on('start', cb);
});

This revision returns:

❯ gulp
[gulp] Using gulpfile /Users/kevinsuttle/Code/myapp/gulpfile.js
[gulp] Starting 'sass'...
[gulp] Starting 'nodemon'...
[gulp] Finished 'sass' after 8.74 ms
[gulp] [nodemon] v1.0.17
[gulp] [nodemon] to restart at any time, enter `rs`
[gulp] [nodemon] watching: *.*
[gulp] [nodemon] starting `node app.js`
[gulp] Finished 'nodemon' after 18 ms
[gulp] Starting 'browser-sync'...
[gulp] Finished 'browser-sync' after 3.65 ms
[gulp] Starting 'default'...
[gulp] Finished 'default' after 8.98 ms
[BS] Proxy running. Use this URL: http://x.xx.xxx.xx:3002
Listening on port 8080

Then a few minutes later:

[gulp] [nodemon] restarting due to changes...
[gulp] [nodemon] starting `node app.js`
[gulp] 'nodemon' errored after 11 min task completion callback called too many times
Listening on port 8080

http://localhost:8080/ - No data received
http://x.xx.xxx.xx:3002/ - Cannot GET '/'

I added my main server file:
https://gist.github.com/kevinSuttle/c8b198aaa30349088c35

can you access your express site through 'localhost:8080' ?

Nope. "No data received".