1. revert nodejs version since latest version is not used by vscode.

2. update gulp to version 4

Author: andxu

gulpfile.js

@@ -15,7 +15,7 @@ gulp.task('build_server', ()=>
 {
   cp.execSync(mvnw()+ ' clean package', {cwd:server_dir, stdio:[0,1,2]} );
 
-  gulp.src(server_dir + '/com.microsoft.jdtls.ext.core/target/com.microsoft.jdtls.ext.core*.jar')
+  return gulp.src(server_dir + '/com.microsoft.jdtls.ext.core/target/com.microsoft.jdtls.ext.core*.jar')
 		.pipe(gulp.dest('./server'))
 });