Correct misleading derivatives in compute issue (#192)

The issue resolution was a relic of a previous version of the spec.
It did not reflect the current spec text, which may have misled some
readers. The resolution now reflects the current spec language.

d3d/HLSL_SM_6_6_Derivatives.md

@@ -289,12 +289,10 @@ are supported if the appropriate capability bit is true.
 Quad Read functions should be supported on Shader Model 6.0
 
 4. How should the quads be ordered?
-   - RESOLVED: Group Index.
-This has advantages and drawbacks.
-It introduces a restriction that the thread group
-must be traversed in row-order.
-Without it, there is no way to identify where the current
-quad is in the group.
+   - RESOLVED: Implementation dependent.
+This spec takes no position on the ordering of quads within a group.
+This gives the most flexibility to implementations possible
+while still presenting a consistent ordering for threads within a single quad.
 
 ---
 # Change Log