[ninja] update ninja repository url

Change-Id: I60f484a709881f035dc90562658b0a598334451f
Reviewed-on: https://chromium-review.googlesource.com/c/1358031
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Fumitoshi Ukai <ukai@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>

ninja

@@ -12,7 +12,7 @@ cat <<-EOF
 No prebuilt ninja binary was found for this system.
 Try building your own binary by doing:
   cd ~
-  git clone https://github.com/martine/ninja.git -b v1.8.2
+  git clone https://github.com/ninja-build/ninja.git -b v1.8.2
   cd ninja && ./configure.py --bootstrap
 Then add ~/ninja/ to your PATH.
 EOF