[Helicopter] Reduce flickering

[GopherTheCoder]

#29 Create "Update" function. In Update, erase only the non-overlapping part between new frame & old frame, then Render the new frame. Using Update instead of Erase then Render, can reduce the amount of I/O if there's overlapping between two frames.

[GopherTheCoder]

@dotnet-policy-service agree

[ZacharyPatten]

Thank you for your interest in contributing. :) I will review this pull request as soon as can.