Fix Jason Ekstrand's name in the contributor list

Author: cubanismo

appendices/VK_EXT_present_timing.txt

@@ -16,7 +16,7 @@ include::{generated}/meta/{refprefix}VK_EXT_present_timing.txt[]
   - Daniel Stone, Collabora
   - Daniel Vetter, Intel
   - Aric Cyr, AMD
-  - Jason Eckstrand, Intel
+  - Jason Ekstrand, Intel
   - Nicolai Hähnle, AMD
   - Alon Or-Bach, Samsung
   - Niklas Smedberg, Unity Technologies