gulpfile.js

var run = require('gulp-run');

var upload_to_shopify = function( file ){
  var splitPath = file.path.split('theme/').pop();
  run('theme upload ' + splitPath, { cwd: 'theme' }).exec();
};



gulp.task( 'watch', function( evnt ) {

  // ADD LINES BELOW TO YOUR WATCH TASK & CHANGE THE './theme/**/*' to the path of your shopify theme
	gulp.watch('./theme/**/*', function(evnt) {
 		upload_liquid(evnt.path);
	});

});