[Wp/Doc] fix typo in option name

src/plugins/wp/doc/manual/wp_plugin.tex

@@ -1455,7 +1455,7 @@ several categories of formatters (PO stands for \emph{Proof Obligations}):
 can be written \verb+"%.."+ or \verb+"%{..}"+. When \verb+range+ is used
 instead of \verb+steps+, the maximal number $n$ of steps is printed as a range $a..b$ that
 contains $n$.
-When option \verb+-report-json+ is used, the previous rank $a$ and $b$ are kept when
+When option \verb+-wp-report-json+ is used, the previous rank $a$ and $b$ are kept when
 available and still fits with the new maximal step number. Otherwise, $a$ and $b$ are re-adjusted
 following an heurisitics designed to increase the stability for non-regression testing.