Update M252 platform name

Author: cyliangtw

src/mbed_os_tools/detect/platform_database.py

@@ -237,7 +237,7 @@
         u"1306": u"NUMAKER_PFM_NANO130",
         u"1307": u"NUMAKER_PFM_NUC240",
         u"1308": u"NUMAKER_IOT_M487",
-        u"1309": u"NUMAKER_M252KG",
+        u"1309": u"NUMAKER_IOT_M252",
         u"1310": u"NUMAKER_IOT_M263A",
         u"1500": u"RHOMBIO_L476DMW1K",
         u"1549": u"LPC1549",