docs: typo (fixes #1376)

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

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

@@ -1179,7 +1179,7 @@ \subsubsection{Positioning Nodes Using Anchors}
 \pgfname\ uses a so-called anchoring mechanism to give you a very fine control
 over the placement. The idea is simple: Imagine a node of rectangular shape of
 a certain size. \pgfname\ defines numerous anchor positions in the shape. For
-example to upper right corner is called, well, not ``upper right anchor'', but
+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}).