Update README.markdown

fix a clerical error of sample in document of zUnion

Author: milkliker

README.markdown

@@ -2110,8 +2110,8 @@ $redis->zAdd('k2', 3, 'val3');
 $redis->zUnion('ko1', array('k1', 'k2')); /* 4, 'ko1' => array('val0', 'val1', 'val2', 'val3') */
 
 /* Weighted zUnion */
-$redis->zUnion('ko2', array('k1', 'k2'), array(1, 1)); /* 4, 'ko1' => array('val0', 'val1', 'val2', 'val3') */
-$redis->zUnion('ko3', array('k1', 'k2'), array(5, 1)); /* 4, 'ko1' => array('val0', 'val2', 'val3', 'val1') */
+$redis->zUnion('ko2', array('k1', 'k2'), array(1, 1)); /* 4, 'ko2' => array('val0', 'val1', 'val2', 'val3') */
+$redis->zUnion('ko3', array('k1', 'k2'), array(5, 1)); /* 4, 'ko3' => array('val0', 'val2', 'val3', 'val1') */
 </pre>
 
 ## zInter