Fix gulp task.

build-appveyor.cake

@@ -104,11 +104,13 @@ Task("Compile").Does(() => {
 });
 
 Task("Gulp").Does(() => {
-	Cake.Npm
+	NpmInstall(new NpmInstallSettings {
-		.WithLogLevel(NpmLogLevel.Silent)
+		LogLevel = NpmLogLevel.Silent,
-		.FromPath(".")
+		WorkingDirectory = "./",
-			.Install()
+		Production = true
-			.RunScript("build");
+	});
+	
+	NpmRunScript("build");
 });
 
 Task("PackageMono").Does(() => {
@@ -308,4 +310,4 @@ Task("Artifacts")
 
 // Run
 RunTarget("Build");
-RunTarget("Artifacts");
+RunTarget("Artifacts");