catch exceptions as const

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: If8dcf70005aebd4ca633b91d6f96badf4a5cd326
diff --git a/callout.cpp b/callout.cpp
index 6c96455..3f409f9 100644
--- a/callout.cpp
+++ b/callout.cpp
@@ -161,7 +161,7 @@
 
         iarchive(*this);
     }
-    catch (std::exception& e)
+    catch (const std::exception& e)
     {
         log<level::ERR>(e.what());
         log<level::ERR>("Failed trying to restore a Callout object",