package/tk: bump to version 8.6.15

For release note, see:
https://sourceforge.net/projects/tcl/files/Tcl/8.6.15/tcltk-release-notes-8.6.15.txt

Note: commit 1af4eae90 "package/tcl: bump version to 8.6.15" updated
the tcl package. This commit updates the tk package, which is released
alongside tcl.

Signed-off-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/tk/tk.hash

@@ -1,3 +1,3 @@
 # Locally calculated
-sha256  8ffdb720f47a6ca6107eac2dd877e30b0ef7fac14f3a84ebbd0b3612cee41a94  tk8.6.14-src.tar.gz
+sha256  550969f35379f952b3020f3ab7b9dd5bfd11c1ef7c9b7c6a75f5c49aca793fec  tk8.6.15-src.tar.gz
 sha256  2cde822b93ca16ae535c954b7dfe658b4ad10df2a193628d1b358f1765e8b198  license.terms

package/tk/tk.mk

@@ -5,7 +5,7 @@
 ################################################################################
 
 TK_VERSION_MAJOR = 8.6
-TK_VERSION = $(TK_VERSION_MAJOR).14
+TK_VERSION = $(TK_VERSION_MAJOR).15
 TK_SOURCE = tk$(TK_VERSION)-src.tar.gz
 TK_SITE = http://downloads.sourceforge.net/project/tcl/Tcl/$(TK_VERSION)
 TK_LICENSE = TCL