File Box2D-fix-version-2.3.1.patch of Package Box2D

--- CMakeLists.txt.orig	2014-04-06 02:43:12.000000000 +0200
+++ CMakeLists.txt	2015-12-16 20:57:28.800666424 +0100
@@ -14,7 +14,7 @@
 option(BOX2D_BUILD_STATIC "Build Box2D static libraries" ON)
 option(BOX2D_BUILD_EXAMPLES "Build Box2D examples" ON)
 
-set(BOX2D_VERSION 2.3.0)
+set(BOX2D_VERSION 2.3.1)
 set(LIB_INSTALL_DIR lib${LIB_SUFFIX})
 
 # The Box2D library.