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

diff --git a/docs/harfbuzz-docs.xml b/docs/harfbuzz-docs.xml
index 12df833..5182bc5 100644
--- a/docs/harfbuzz-docs.xml
+++ b/docs/harfbuzz-docs.xml
@@ -22,7 +22,7 @@
         source tree is available
         <ulink url="http://cgit.freedesktop.org/harfbuzz/">here</ulink>.
         Also available on
-        <ulink url="https://github.com/behdad/harfbuzz">github</ulink>.
+        <ulink url="https://github.com/harfbuzz/harfbuzz">github</ulink>.
         See <xref linkend="download" endterm="download.title"/> for release tarballs.
       </para>
       <para>