docs: mark ARB_gpu_shader_fp64 as done in core

No driver support... yet. But core is ready.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
diff --git a/docs/GL3.txt b/docs/GL3.txt
index 6cb40ed..3a46700 100644
--- a/docs/GL3.txt
+++ b/docs/GL3.txt
@@ -109,7 +109,7 @@
   - Enhanced per-sample shading                        DONE (r600)
   - Interpolation functions                            DONE (r600)
   - New overload resolution rules                      DONE
-  GL_ARB_gpu_shader_fp64                               started (Dave)
+  GL_ARB_gpu_shader_fp64                               DONE ()
   GL_ARB_sample_shading                                DONE (i965, nv50, nvc0, r600, radeonsi)
   GL_ARB_shader_subroutine                             not started
   GL_ARB_tessellation_shader                           started (Chris, Ilia)