manual: correct value of prior_trunc used in code

(cherry picked from commit 54409c08)

doc/manual/source/the-model-file.rst

@@ -6940,9 +6940,9 @@ observed variables.
     .. option:: prior_trunc = DOUBLE
-       Probability of extreme values of the prior density that is
+       Probability of extreme values of the prior density in each tail that is
        ignored when computing bounds for the parameters. Default:
-       ``1e-32``.
+       ``1e-10``.
     .. option:: huge_number = DOUBLE