sdl2: security bump to version 2.0.7

Fixes CVE-2017-2888 - An exploitable integer overflow vulnerability exists
when creating a new RGB Surface in SDL 2.0.5.  A specially crafted file can
cause an integer overflow resulting in too little memory being allocated
which can lead to a buffer overflow and potential code execution.  An
attacker can provide a specially crafted image file to trigger this
vulnerability.

Also add a hash for the license file while we're at it.

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

package/sdl2/sdl2.hash

@@ -1,2 +1,4 @@
-# Locally calculated after checking http://www.libsdl.org/release/SDL2-2.0.6.tar.gz.sig
-sha256 03658b5660d16d7b31263a691e058ed37acdab155d68dabbad79998fb552c5df  SDL2-2.0.6.tar.gz
+# Locally calculated after checking http://www.libsdl.org/release/SDL2-2.0.7.tar.gz.sig
+sha256 ee35c74c4313e2eda104b14b1b86f7db84a04eeab9430d56e001cea268bf4d5e  SDL2-2.0.7.tar.gz
+# Locally calculated
+sha256 bbd2edb1789c33de29bb9f8d1dbe2774584a9ce8c4e3162944b7a3a447f5e85d  COPYING.txt

package/sdl2/sdl2.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-SDL2_VERSION = 2.0.6
+SDL2_VERSION = 2.0.7
 SDL2_SOURCE = SDL2-$(SDL2_VERSION).tar.gz
 SDL2_SITE = http://www.libsdl.org/release
 SDL2_LICENSE = Zlib