Fix gulpfile to use gulp 4 API

js/gulpfile.js

@@ -144,7 +144,7 @@ function getClosureBuilderCommand(exportsFile, outputFile) {
   exportsFile  + ' > ' + outputFile;
 }
 
-gulp.task('dist', ['genproto_wellknowntypes'], function (cb) {
+gulp.task('dist', gulp.series(['genproto_wellknowntypes'], function (cb) {
   // TODO(haberman): minify this more aggressively.
   // Will require proper externs/exports.
   exec(getClosureBuilderCommand('commonjs/export.js', 'google-protobuf.js'),
@@ -153,7 +153,7 @@ gulp.task('dist', ['genproto_wellknowntypes'], function (cb) {
     console.log(stderr);
     cb(err);
   });
-});
+}));
 
 gulp.task('commonjs_asserts', function (cb) {
   exec('mkdir -p commonjs_out/test_node_modules && ' +
@@ -179,7 +179,7 @@ gulp.task('commonjs_testdeps', function (cb) {
   });
 });
 
-gulp.task('make_commonjs_out', ['dist', 'genproto_well_known_types_commonjs', 'genproto_group1_commonjs', 'genproto_group2_commonjs', 'genproto_commonjs_wellknowntypes', 'commonjs_asserts', 'commonjs_testdeps', 'genproto_group3_commonjs_strict'], function (cb) {
+gulp.task('make_commonjs_out', gulp.series(['dist', 'genproto_well_known_types_commonjs', 'genproto_group1_commonjs', 'genproto_group2_commonjs', 'genproto_commonjs_wellknowntypes', 'commonjs_asserts', 'commonjs_testdeps', 'genproto_group3_commonjs_strict'], function (cb) {
   // TODO(haberman): minify this more aggressively.
   // Will require proper externs/exports.
   var cmd = "mkdir -p commonjs_out/binary && mkdir -p commonjs_out/test_node_modules && ";
@@ -201,35 +201,35 @@ gulp.task('make_commonjs_out', ['dist', 'genproto_well_known_types_commonjs', 'g
     console.log(stderr);
     cb(err);
   });
-});
+}));
 
-gulp.task('deps', ['genproto_well_known_types_closure', 'genproto_group1_closure', 'genproto_group2_closure'], function (cb) {
+gulp.task('deps', gulp.series(['genproto_well_known_types_closure', 'genproto_group1_closure', 'genproto_group2_closure'], function (cb) {
   exec('./node_modules/google-closure-library/closure/bin/build/depswriter.py binary/arith.js binary/constants.js binary/decoder.js binary/encoder.js binary/reader.js binary/utils.js binary/writer.js debug.js map.js message.js node_loader.js test_bootstrap.js > deps.js',
        function (err, stdout, stderr) {
     console.log(stdout);
     console.log(stderr);
     cb(err);
   });
-});
+}));
 
-gulp.task('test_closure', ['genproto_well_known_types_closure', 'genproto_group1_closure', 'genproto_group2_closure', 'deps'], function (cb) {
+gulp.task('test_closure', gulp.series(['genproto_well_known_types_closure', 'genproto_group1_closure', 'genproto_group2_closure', 'deps'], function (cb) {
   exec('JASMINE_CONFIG_PATH=jasmine.json ./node_modules/.bin/jasmine',
        function (err, stdout, stderr) {
     console.log(stdout);
     console.log(stderr);
     cb(err);
   });
-});
+}));
 
-gulp.task('test_commonjs', ['make_commonjs_out'], function (cb) {
+gulp.task('test_commonjs', gulp.series(['make_commonjs_out'], function (cb) {
   exec('cd commonjs_out && JASMINE_CONFIG_PATH=jasmine.json NODE_PATH=test_node_modules ../node_modules/.bin/jasmine',
        function (err, stdout, stderr) {
     console.log(stdout);
     console.log(stderr);
     cb(err);
   });
-});
+}));
 
-gulp.task('test', ['test_closure', 'test_commonjs'], function(cb) {
+gulp.task('test', gulp.series(['test_closure', 'test_commonjs'], function(cb) {
   cb();
-});
+}));