Memory leak problem

I'm using master code build with go 1.13.4，I hava configed 4 kafka cluster，but the memory become larger when burrow started a few hours later. The server total memory 16GB. Nov 05 and Nov 06 I restart burrow.
The storage set below.
```
[storage.default]
class-name="inmemory"
workers=20
intervals=30
expire-group=600
min-distance=1
```

Start by reproducing the reported growth using the provided four-cluster setup and the [storage.default] configuration. Monitor Burrow's memory over several hours and compare behavior across storage settings; done means identifying a reproducible cause and confirming that memory remains stable after the fix.

Written by the indexing model from the issue text.