Update book.tex

Thanks to Tyler Scott for letting me know about these typos.

Author: AllenDowney

book/book.tex

@@ -4969,9 +4969,9 @@ \section{Conway's conjecture}
 \label{chap06-4}
 \end{figure}
 
-But there are a some simple starting conditions that 
+But there are some simple starting conditions that 
 yield a surprising number of live cells, and take a
-long time to settle down.  Because these patterns are cso long-lived, they
+long time to settle down.  Because these patterns are so long-lived, they
 are called ``Methuselahs''.
 
 \index{Methuselah}