gulp task for reading git SHA1

gulp_task_git_command.js

gulp.task('add:deployment', function (cb) {
    var command = 'git rev-parse HEAD';
    var deploymentFile = 'source/js/common/deployment.js';
    exec(command, function (err, stdout, stderr) {
        if(err) {
            cb(err);
            gutil.log("Executing '" + command + " fails");
            throw new Error("error occured while executing command " + command);
        }
        var jsCode = "window.deploymentNumber = " + stdout;
        fs.writeFile(deploymentFile, jsCode, function(err) {
            if(err) {
                gutil.log("Writing file " + deploymentFile);
                throw new Error("error occured while executing command " + command);
            }
            gutil.log("Deployment number " + stdout + " is written to file " + deploymentFile);
        });
    });
})