Build: Fix datepicker demo in dist

Closes #8475

Author: apsdehal

build/tasks/alias.js

@@ -41,7 +41,8 @@ grunt.registerTask( "build:demos", [
 	"copy:demos.processed",
 	"copy:demos.php",
 	"copy:demos.unprocessed",
-	"copy:demos.backbone"
+	"copy:demos.backbone",
+	"copy:demos.datepicker"
 ] );
 grunt.registerTask( "build:cdn", [
 	"copy:jqueryCDN",

build/tasks/options/copy.js

@@ -247,6 +247,20 @@ return {
 			}
 		]
 	},
+	"demos.datepicker": {
+		files: [
+			{
+				expand: true,
+				src: [ "external/jquery-mobile-datepicker-wrapper/**/*" ],
+				dest: path.join( "<%= dist %>" )
+			},
+			{
+				expand: true,
+				src: [ "external/jquery-ui/widgets/datepicker.js" ],
+				dest: path.join( "<%= dist %>" )
+			}
+		]
+	},
 	"demos.unprocessed": {
 		files: [
 			{