Use String.slice instead of String.substring in order to save a three…

… bytes. Close gh-1261.

src/data.js

@@ -238,7 +238,7 @@ jQuery.fn.extend({
						name = attrs[ i ].name;

						if ( name.indexOf( "data-" ) === 0 ) {
							name = jQuery.camelCase( name.substring(5) );
							name = jQuery.camelCase( name.slice(5) );
							dataAttr( elem, name, data[ name ] );
						}
					}