Fix supervisor doc: Shutdown, MaxR and MaxT type specs

The next code snippets from supervisor.erl show that Shutdown from a
child specification must be greater than zero and the same applies to
MaxT.

--- supervisor.erl ----------------------------------------------------------
validShutdown(Shutdown, _)
  when is_integer(Shutdown), Shutdown > 0 -> true;
validShutdown(infinity, _)             -> true;
validShutdown(brutal_kill, _)          -> true;
validShutdown(Shutdown, _)             -> throw({invalid_shutdown, Shutdown}).

validIntensity(Max) when is_integer(Max),
                         Max >=  0 -> true;
validIntensity(What)               -> throw({invalid_intensity, What}).

validPeriod(Period) when is_integer(Period),
                         Period > 0 -> true;
validPeriod(What)                   -> throw({invalid_period, What}).
-----------------------------------------------------------------------------

1 files changed, 1 insertions, 1 deletions

diff --git a/system/doc/design_principles/sup_princ.xml b/system/doc/design_principles/sup_princ.xml
index c473e257fa..353430752c 100644
--- a/system/doc/design_principles/sup_princ.xml
+++ b/system/doc/design_principles/sup_princ.xml
@@ -136,7 +136,7 @@ init(...) ->
         M = F = atom()
         A = [term()]
     Restart = permanent | transient | temporary
-    Shutdown = brutal_kill | integer()>=0 | infinity
+    Shutdown = brutal_kill | integer()>0 | infinity
     Type = worker | supervisor
     Modules = [Module] | dynamic
         Module = atom()]]></code>