The input parameters to this function are both type `string` and `crypto:md5` accepts `iolist` or `binary`, but the local `md5` only accepts `binary`. This causes the following test failure:

```
riak_cs_utils_test: bucket_resolution_test...*failed*
in function riak_cs_utils:md5_update/2 (src/riak_cs_utils.erl, line 476)
  called as md5_update(<<1,35,69,103,137,171,205,239,254,220,186,152,118,84,...>>,"festersquest")
in call from riak_cs_utils:md5/1 (src/riak_cs_utils.erl, line 467)
in call from riak_cs_utils:generate_canonical_id/2 (src/riak_cs_utils.erl, line 1181)
in call from riak_cs_utils:user_record/5 (src/riak_cs_utils.erl, line 1391)
in call from riak_cs_utils_test:bucket_resolution_test/0 (test/riak_cs_utils_test.erl, line 246)
**error:function_clause
```