Fix eps image path for some versions of epstopdf.

docs/developer-guide/library-design/library-design.tex

@@ -38,7 +38,7 @@ in the core sub-libraries, is depicted in the Figure~\ref{f:library:overview}.
 
 \begin{figure}
 \centering
-\includegraphics[width=0.6\textwidth]{img/architecture}
+\includegraphics[width=0.6\textwidth]{library-design/img/architecture}
 \caption{Structural overview of the Nektar++ libraries}
 \label{f:library:structure}
 \end{figure}