[infer] fix OCaml formatting

infer/src/backend/symExec.ml

@@ -1068,7 +1068,7 @@ and add_constraints_on_retval pdesc prop ret_ids ret_type_option callee_pname =
           else
           if !Config.footprint then
             let (prop', fresh_fp_var) = add_to_footprint abducted_ret_pv ret_typ prop in
-            let prop'' = Prop.conjoin_eq ~footprint:true (Sil.Var ret_id) fresh_fp_var prop' in
+            let prop'' = Prop.conjoin_eq ~footprint: true (Sil.Var ret_id) fresh_fp_var prop' in
             add_ret_non_null ret_id ret_typ prop''
           else
             (* find an hpred [abducted_pvar] |-> A in [prop] and add [exp] = A to prop *)