docs: correct a reference to anchor list (fixes #1377)

Signed-off-by: Yukai Chou <[email protected]>

doc/generic/pgf/pgfmanual-en-tikz-shapes.tex

@@ -1182,7 +1182,7 @@ \subsubsection{Positioning Nodes Using Anchors}
 example the upper right corner is called, well, not ``upper right anchor'', but
 the |north east| anchor of the shape. The center of the shape has an anchor
 called |center| on top of it, and so on. Here are some examples (a complete
-list is given in Section~\ref{section-the-shapes}).
+list for predefined shapes is given in Section~\ref{section-predefined-shapes}).
 
 \medskip\noindent
 \begin{tikzpicture}