message: use C++14 enable_if_t

Avoid the `enable_if<...>::type` and use the preferred C++14
`enable_if_t` short-hand.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I139fb826051c922c56b8310c53a4787b630604cb
diff --git a/include/sdbusplus/message/append.hpp b/include/sdbusplus/message/append.hpp
index b67e4a6..284146d 100644
--- a/include/sdbusplus/message/append.hpp
+++ b/include/sdbusplus/message/append.hpp
@@ -88,7 +88,7 @@
 // std::vector/map/unordered_map/set need loops
 template <typename T>
 struct can_append_multiple<
-    T, typename std::enable_if<utility::has_const_iterator<T>::value>::type> :
+    T, typename std::enable_if_t<utility::has_const_iterator<T>::value>> :
     std::false_type
 {};
 // std::pair needs to be broken down into components.
diff --git a/include/sdbusplus/message/read.hpp b/include/sdbusplus/message/read.hpp
index 09252ee..f13d3ae 100644
--- a/include/sdbusplus/message/read.hpp
+++ b/include/sdbusplus/message/read.hpp
@@ -91,9 +91,8 @@
 // std::vector/map/unordered_vector/set need loops
 template <typename T>
 struct can_read_multiple<
-    T,
-    typename std::enable_if<utility::has_emplace_method<T>::value ||
-                            utility::has_emplace_back_method<T>::value>::type> :
+    T, typename std::enable_if_t<utility::has_emplace_method<T>::value ||
+                                 utility::has_emplace_back_method<T>::value>> :
     std::false_type
 {};