paper: Fix citation [4] -> [2].

doc/paper/2023/simhydro/paper.txt

@@ -14,7 +14,7 @@ Numerous tools are available to simulate river flow. Among them, one-dimensional
     • Multi-platform Windows, Unix-like,
     • no dependence on an external graphics library with a paid license for user, 
     • generate as much code as possible from a UML diagram.
-Now, PAMHyR suffers from complexity due to highly specific interface, as well as a significant technological debt [4]: old external library no longer maintained, over dated project architecture, and numerous modifications by multiple developers (and internship) over short periods of time, with no vision of long-term maintainability. What's more, the software is only in French and the code is closed (the sources are not available), which is a hindrance to the notoriety of the software as well as to the vitality of development. In addition, no significant changes have been made in the application since 2016, even if PAMHyR is still often used for river modeling [4].
+Now, PAMHyR suffers from complexity due to highly specific interface, as well as a significant technological debt [4]: old external library no longer maintained, over dated project architecture, and numerous modifications by multiple developers (and internship) over short periods of time, with no vision of long-term maintainability. What's more, the software is only in French and the code is closed (the sources are not available), which is a hindrance to the notoriety of the software as well as to the vitality of development. In addition, no significant changes have been made in the application since 2016, even if PAMHyR is still often used for river modeling [2].
 INRAE needs a new tool to keep up with today’s technologies and with the development of its numerical solvers. In this paper we introduce the current work on the new graphical user interface Pamhyr2.
 2.	Objective
 2.1	History and need