Update for the Facebook Adapter from 5.5.1.0 to 5.6.0.0 causes iOS12 crash on the second app-start

[ksloginov]

We're recently updated the pod of GoogleMobileAdsMediationFacebook from 5.5.1.0 to 5.6.0.0 and every iOS12 crashes now on the second start (just clean install, close the app and try to open again)

(55714,0x11216ddc0) malloc: double free for ptr 0x7f8a29854e00
(55714,0x11216ddc0) malloc: *** set a breakpoint in malloc_error_break to debug

Pod file:

....
pod 'Firebase/AdMob', '>6.13.0'
pod 'FBSDKLoginKit/Swift', '>5.11.1'
pod 'GoogleMobileAdsMediationFacebook', '~>5.6.0.0'
....

I wish I could give more details on that - but hopefully this should be enough. For now - we've rolled back to stable 5.5.1.0 version (there client works as expected)