boltdb package is unmaintained with memory issues

[AbdelrahmanElawady]

for example:

• [master] panic if use hashicorp with -race detect seaweedfs/seaweedfs#3521
• runtime with -race: fatal error: checkptr: converted pointer straddles multiple allocations golang/go#54690

https://github.com/etcd-io/bbolt seems to be a good replacement