Set default mapping for gcc62 compiler to help asetup pick the correct...

Set default mapping for gcc62 compiler to help asetup pick the correct compiler version from the right place.

External/AtlasCompilers/compilers.json

@@ -2,7 +2,7 @@
 	"gcc_config_version": {
 		"gcc48": "4.8.4",
 		"gcc49": "4.9.3",
-		"gcc52": "5.2.0"
+		"gcc62": "6.2.0"
 	},
 	"clang_config_version": {
 		"clang37": "3.7"