Crash: [FSnapshotHolder updateSnapshot:withNewSnapshot:]

[saldous]

• Xcode version: _9.1
• Firebase SDK version: _4.6.0

Crashlytics is reporting a number of crashes in my app since updating to Firebase 4.6.0.

[FSnapshotHolder updateSnapshot:withNewSnapshot:]

Fatal Exception: NSInvalidArgumentException
-[FListenProvider updateChild:withNewChild:]: unrecognized selector sent to instance 0x1c042da40

[paulb777]

Duplicate of #281