fix: remove the trailing comma after the last SKU (frappe#201)

Instead of using the reduce() method to explode the list of SKUs into separate objects, we can use the map() method and get rid of the trailing comma after the last SKU

ecommerce_integrations/shopify/page/shopify_import_products/shopify_import_products.js

@@ -174,7 +174,7 @@ shopify.ProductImporter = class {
 				// 'Image': product.image && product.image.src && `<img style="height: 50px" src="${product.image.src}">`,
 				'ID': product.id,
 				'Name': product.title,
-				'SKUs': product.variants && product.variants.reduce((a, b) => a + `${b.sku}, `, ''),
+				'SKUs': product.variants && product.variants.map(a => `${a.sku}`).join(', '),
 				'Status': this.getProductSyncStatus(product.synced),
 				'Action': !product.synced ? `<button type="button" class="btn btn-default btn-xs btn-sync mx-2" data-product="${product.id}"> Sync </button>` : '-',
 			}));