Correct off-by-one error in range of 64 bit int. Also, Racket fixnums are not 64 bit.

book.tex

@@ -338,8 +338,9 @@ according to the left-hand-side. (We do not define $\Int$ because the
 reader already knows what an integer is.) We make the simplifying
 design decision that all of the languages in this book only handle
 machine-representable integers (those representable with 64-bits,
-i.e., the range $-2^{63}$ to $2^{63}$) which corresponds to the
-\texttt{fixnum} datatype in Racket. A name such as $\Exp$ that is
+i.e., the range $-2^{63}$ to $2^{63}-1$)
+ which is similar to the \texttt{fixnum} datatype in Racket.
+A name such as $\Exp$ that is
 defined by the grammar rules is a \emph{non-terminal}.
 
 The second grammar rule is the \texttt{read} operation that receives