package/go: security bump to version 1.13.15

Fixes the following security issue:

CVE-2020-16845: Go before 1.13.15 and 14.x before 1.14.7 can have an
infinite read loop in ReadUvarint and ReadVarint in encoding/binary via
invalid inputs

https://github.com/golang/go/issues/40620

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/go/go.hash

@@ -1,3 +1,3 @@
 # From https://golang.org/dl/
-sha256	197333e97290e9ea8796f738d61019dcba1c377c2f3961fd6a114918ecc7ab06  go1.13.14.src.tar.gz
+sha256	5fb43171046cf8784325e67913d55f88a683435071eef8e9da1aa8a1588fcf5d  go1.13.15.src.tar.gz
 sha256	2d36597f7117c38b006835ae7f537487207d8ec407aa9d9980794b2030cbc067  LICENSE

package/go/go.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-GO_VERSION = 1.13.14
+GO_VERSION = 1.13.15
 GO_SITE = https://storage.googleapis.com/golang
 GO_SOURCE = go$(GO_VERSION).src.tar.gz