catch exceptions as const

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Id5a06698ddd6f91510a34aaf9df535bd34c099c0
diff --git a/serialize.hpp b/serialize.hpp
index 32648e2..4bae397 100644
--- a/serialize.hpp
+++ b/serialize.hpp
@@ -86,7 +86,7 @@
                 iarchive(object);
             }
         }
-        catch (cereal::Exception& e)
+        catch (const cereal::Exception& e)
         {
             phosphor::logging::log<phosphor::logging::level::ERR>(e.what());
             fs::remove(p);