Update gulp scripts to v4

Author: jozefizso

src/gitattributes.csproj

@@ -15,8 +15,8 @@
   </ItemGroup>
 
   <Target Name="PrepublishScript" BeforeTargets="PrepareForPublish">
-    <Exec Command="npm install" />
-    <Exec Command="gulp build" />
+    <Exec Command="npm ci" />
+    <Exec Command="npm run build" />
   </Target>
 
   <ItemGroup>

src/gulpfile.js

@@ -18,5 +18,7 @@ function copy() {
 };
 
 const build = gulp.series(clean, copy);
-gulp.task('build', build);
-gulp.task('default', build);
+
+exports.build = build;
+exports.clean = clean;
+exports.default = build;