ERP031 Documentation inconsistent with the actual case

The [documentation ERP031](https://github.com/SergeyTeplyakov/ErrorProne.NET/blob/ca6b4ddea3b2cade7901b64842fd800851d0d6b9/docs/Rules/ERP031.md) is inconistent with the ERP031.

ERP031 is trigger when a usage of some specific linq is done on an ConcurrentDictionary. 
The documentation shows an ERP031 triggered when a non-thread-safe collection is used.
