Correct shards sorting problem

In sensei-hadoop-indexing project, when creating shards it will sort the shardNames, but the current sorting method has a problem:

Suppose there are 20 shards, and their names are:
shard0, shard1,shard2,shard3...shard19

current sorted result:
[shard0, shard1, shard11, shard12...shard19, shard2,shard3...shard9]

but the expected sorted result should be:
[shard0, shard1, shard2, shard3...shard10 ... shard19]