Update version number to v3.1.5

include/rtdef.h

@@ -49,7 +49,7 @@ extern "C" {
 /* RT-Thread version information */
 #define RT_VERSION                      3L              /**< major version number */
 #define RT_SUBVERSION                   1L              /**< minor version number */
-#define RT_REVISION                     4L              /**< revise version number */
+#define RT_REVISION                     5L              /**< revise version number */
 
 /* RT-Thread version */
 #define RTTHREAD_VERSION                ((RT_VERSION * 10000) + \