fix typo: Unknown pseudo selector 'lsat-child'. renamed to 'last-child'. (#601)

Author: azataiot

content/tutorial/common/src/app.html

@@ -183,7 +183,7 @@
 				margin-top: 0;
 			}
 
-			progress:lsat-child {
+			progress:last-child {
 				margin-bottom: 0;
 			}