Rename kReachabilityChangedNotification

[picciano]

This is a popular class to include in client apps. By including it in the libMapboxGL.a , but not including the header in the Headers directory prevents client app from using it. Also, if a client tries to include its own version of reachability, duplicate symbols build errors are the result.

[1ec5]

#759 renamed Mapbox GL’s copy of Reachability to MGLReachability, which allows the client to include their own version of Reachability without triggering duplicate symbol warnings. Reachability is a dependency of Mapbox GL but kind of out of scope for its public API.

[picciano]

Looks like the problem comes from this const in reachability.h:
extern NSString *const kReachabilityChangedNotification;

The workaround would either be for the client app to rename this, or rename the one in MGLReachability.