Another bug fix and Credits correction

This update was mainly to address yet another bug in the game, whereby if you happened to be standing where the exit would appear when you collected the last collectible, it would not register and when you moved it would *erase* the exit door! Now, the game will automatically detect the door over you and finish the level.

However, I also took the chance to correct the game Credits sequence. I've since found out that "Colin the Cleaner" from 1987 was in fact a direct ripoff of an earlier game from the cover of Spectrum Computing magazine, called "Ralph on Alpha 2". The authors were Darren Farmer and Andrew Dunne.

The Harry S Price of this version simply lifted their code, reskinned the graphics and renamed the game Colin The Cleaner - then sold this to a (presumably clueless and/or morally bankrupt) publisher, who took it without question!

Link to the original game details here:

https://spectrumcomputing.co.uk/entry/16728/ZX-Spectrum/Ralph_on_Alpha_2

I thought it was important, especially given my recent modifications to the game, to update this in the title credits so as to be accurate to the game's history. Mr Price is still in there, but with a somewhat more accurate (and less flattering) representation.

I hope this clears things up for posterity - while making the game a little more polished too!