Update voxel/audio-* CMakeLists to 3.8 (#315)

These were missed since they hadn't been bumped to 3.1

examples/audio-test/CMakeLists.txt

diff --git a/examples/audio-test/CMakeLists.txt b/examples/audio-test/CMakeLists.txt
index 81819bc..def6d74 100644
--- a/examples/audio-test/CMakeLists.txt
+++ b/examples/audio-test/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 2.8.9)

-project (tilt)

+cmake_minimum_required(VERSION 3.8)

+project (audio-test)

 include (../../32blit.cmake)

 blit_executable (audio-test audio-test.cpp)

examples/audio-wave/CMakeLists.txt

diff --git a/examples/audio-wave/CMakeLists.txt b/examples/audio-wave/CMakeLists.txt
index 24d2df1..5918e25 100644
--- a/examples/audio-wave/CMakeLists.txt
+++ b/examples/audio-wave/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 2.8.9)

+cmake_minimum_required(VERSION 3.8)

 project (audio-wave)

 include (../../32blit.cmake)

 blit_executable (audio-wave audio-wave.cpp)

examples/voxel/CMakeLists.txt

diff --git a/examples/voxel/CMakeLists.txt b/examples/voxel/CMakeLists.txt
index f592d33..937bda2 100644
--- a/examples/voxel/CMakeLists.txt
+++ b/examples/voxel/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 2.8.9)

+cmake_minimum_required(VERSION 3.8)

 project (voxel)

 include (../../32blit.cmake)

 blit_executable (voxel voxel.cpp)