Move all references of old url to the new address (#622)

diff --git a/src/sample.py b/src/sample.py
index c2cb94d..844fa4c 100755
--- a/src/sample.py
+++ b/src/sample.py
@@ -45,7 +45,7 @@
 ## Add text to buffer
 ##
 #
-# See https://github.com/behdad/harfbuzz/pull/271
+# See https://github.com/harfbuzz/harfbuzz/pull/271
 #
 if False:
 	# If you do not care about cluster values reflecting Python