Fix extent in the example in 3.4.5.6, page 26 (#120)

Fixes #119

Co-authored-by: Pavel Kirienko <[email protected]>

Author: Silver Valdvee

specification/dsdl/serializable_types.tex

@@ -475,7 +475,7 @@ \subsubsection{Bit length set}
     \begin{minted}{python}
         # B.1.0
         uint64 x
-        @extent 8 * 8
+        @extent 17 * 8
     \end{minted}
 
     Imagine then that \verb|B.1.0| is replaced with the following:
@@ -484,7 +484,7 @@ \subsubsection{Bit length set}
         # B.1.1
         uint64 x
         bool[<=64] y
-        @extent 8 * 8
+        @extent 17 * 8
     \end{minted}
 
     Once this modification is introduced, the fragile assumption about the alignment of