package/go: security bump to version 1.15.12

Fixes the following security issues:

- CVE-2021-31525: ReadRequest and ReadResponse in net/http can hit an
  unrecoverable panic when reading a very large header (over 7MB on 64-bit
  architectures, or over 4MB on 32-bit ones).  Transport and Client are
  vulnerable and the program can be made to crash by a malicious server.
  Server is not vulnerable by default, but can be if the default max header
  of 1MB is overridden by setting Server.MaxHeaderBytes to a higher value,
  in which case the program can be made to crash by a malicious client.

  https://github.com/golang/go/issues/45710

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

package/go/go.hash

@@ -1,3 +1,3 @@
 # From https://golang.org/dl/
-sha256  f25b2441d4c76cf63cde94d59bab237cc33e8a2a139040d904c8630f46d061e5  go1.15.11.src.tar.gz
+sha256  1c6911937df4a277fa74e7b7efc3d08594498c4c4adc0b6c4ae3566137528091  go1.15.12.src.tar.gz
 sha256	2d36597f7117c38b006835ae7f537487207d8ec407aa9d9980794b2030cbc067  LICENSE

package/go/go.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-GO_VERSION = 1.15.11
+GO_VERSION = 1.15.12
 GO_SITE = https://storage.googleapis.com/golang
 GO_SOURCE = go$(GO_VERSION).src.tar.gz