catch exceptions as const

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: If8dcf70005aebd4ca633b91d6f96badf4a5cd326
diff --git a/policy_table.cpp b/policy_table.cpp
index df32d59..f77bc6e 100644
--- a/policy_table.cpp
+++ b/policy_table.cpp
@@ -68,7 +68,7 @@
 
         loaded = true;
     }
-    catch (std::exception& e)
+    catch (const std::exception& e)
     {
         log<level::ERR>("Failed loading policy table json file",
                         entry("FILE=%s", jsonFile.c_str()),