Typo in ARB_copy_image #385 (#388)

PBTC was used instead of BPTC.
diff --git a/extensions/ARB/ARB_copy_image.txt b/extensions/ARB/ARB_copy_image.txt
index 86fc172..a41dc2e 100644
--- a/extensions/ARB/ARB_copy_image.txt
+++ b/extensions/ARB/ARB_copy_image.txt
@@ -268,7 +268,7 @@
 Dependencies on OpenGL 4.2 and ARB_texture_compression_bptc:
 
     If OpenGL 4.2 or later, and ARB_texture_compression_bptc is not
-    supported, remove any references to the PBTC compressed texture
+    supported, remove any references to the BPTC compressed texture
     formats.
     
 Errors