Fix a few KHR extension links (#89)

They were still pointing to the old txt file.

Signed-off-by: Kevin Petit <kevin.petit@arm.com>
diff --git a/extensions/khr/cl_khr_d3d10_sharing.txt b/extensions/khr/cl_khr_d3d10_sharing.txt
index 2e3f289..cb4876e 100644
--- a/extensions/khr/cl_khr_d3d10_sharing.txt
+++ b/extensions/khr/cl_khr_d3d10_sharing.txt
@@ -9,4 +9,4 @@
 
 The Asciidoc source for this extension may be found here:
 
-https://github.com/KhronosGroup/OpenCL-Docs/blob/master/ext/cl_khr_d3d10_sharing.txt
+https://github.com/KhronosGroup/OpenCL-Docs/blob/master/ext/cl_khr_d3d10_sharing.asciidoc
diff --git a/extensions/khr/cl_khr_gl_sharing.txt b/extensions/khr/cl_khr_gl_sharing.txt
index 893e460..8b85e32 100644
--- a/extensions/khr/cl_khr_gl_sharing.txt
+++ b/extensions/khr/cl_khr_gl_sharing.txt
@@ -9,6 +9,6 @@
 
 The Asciidoc source for this extension may be found here:
 
-https://github.com/KhronosGroup/OpenCL-Docs/blob/master/ext/cl_khr_gl_sharing__context.txt
-https://github.com/KhronosGroup/OpenCL-Docs/blob/master/ext/cl_khr_gl_sharing__memobjs.txt
+https://github.com/KhronosGroup/OpenCL-Docs/blob/master/ext/cl_khr_gl_sharing__context.asciidoc
+https://github.com/KhronosGroup/OpenCL-Docs/blob/master/ext/cl_khr_gl_sharing__memobjs.asciidoc
 
diff --git a/extensions/khr/cl_khr_icd.txt b/extensions/khr/cl_khr_icd.txt
index 6dda605..17b3488 100644
--- a/extensions/khr/cl_khr_icd.txt
+++ b/extensions/khr/cl_khr_icd.txt
@@ -9,4 +9,4 @@
 
 The Asciidoc source for this extension may be found here:
 
-https://github.com/KhronosGroup/OpenCL-Docs/blob/master/ext/cl_khr_icd.txt
\ No newline at end of file
+https://github.com/KhronosGroup/OpenCL-Docs/blob/master/ext/cl_khr_icd.asciidoc