Fix minor typo in pgfmanual-en-gd-usage-tikz.tex

doc/generic/pgf/pgfmanual-en-gd-usage-tikz.tex

@@ -169,7 +169,7 @@ \subsection{Graph Drawing Parameters}
 an algorithm can only try to ``do its best''. While many graph parameters are
 very specific to a single algorithm, a number of graph parameters will be
 important for many algorithms and they are documented in the course of the
-present section. Here is an example of an option the ``always works'':
+present section. Here is an example of an option that ``always works'':
 %
 \begin{codeexample}[preamble={\usetikzlibrary{graphs,graphdrawing}
 \usegdlibrary{force}}]