Use GLSL 420 with extensions in comp_unordered

As this shader was added after the GLSL 420 PR was created, this one was
not present in the change.

Signed-off-by: Tomas Slusny <slusnucky@gmail.com>

runelite-client/src/main/resources/net/runelite/client/plugins/gpu/comp_unordered.glsl

@@ -22,7 +22,10 @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
-#version 430 core
+
+#version 420
+#extension GL_ARB_compute_shader : require
+#extension GL_ARB_shader_storage_buffer_object : require
 
 #include comp_common.glsl