Fix a dead link in CMakeLists.txt

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5e0bc9f..764a41f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -233,7 +233,7 @@
 if (HB_HAVE_ICU)
   add_definitions(-DHAVE_ICU)
 
-  # https://github.com/WebKit/webkit/blob/master/Source/cmake/FindICU.cmake
+  # https://github.com/WebKit/webkit/blob/fdd7733f2f30eab7fe096a9791f98c60f62f49c0/Source/cmake/FindICU.cmake
   find_package(PkgConfig)
   pkg_check_modules(PC_ICU QUIET icu-uc)