Upsize rivets tail hook connection to rib 801

The 4mm rivets were known to have probably sheared in a hard impact tail-down incident. Upsizing to 4.8mm seems prudent. Another reason was that the 4mm holes were quite stretched and deformed in the bending of the tail hook angle, such that the rivet connection could be rather less firm. Upsizjng to 4.8mm completely removes this.

Note also I have upsized the rearmost rivet in the connection to longeron 801 for the same reason.