docs: fix indentation in math example function (#1351)

Author: vog

doc/generic/pgf/pgfmanual-en-library-math.tex

@@ -57,8 +57,8 @@ \subsection{Overview}
     if \n == 0 then {
       return 0;
     } else {
-       return fibonacci2(\n, 0, 1);
-     };
+      return fibonacci2(\n, 0, 1);
+    };
   };
   function fibonacci2(\n, \p, \q) {
     if \n == 1 then {