Fix the mojo.idl link in the README.md

Post rename, there are certain links within README.md file which
are pointing to the old directory structure.  Correct these links
to point to the correct ones!

REVIEWER=mstensho@chromium.org
R=mstensho@chromium.org
Signed-off-by: Vivek Galatage <vivekg@chromium.org>
Change-Id: Ib1148cb4339823081ef96f2e24a87f2f21f57c15
Reviewed-on: https://chromium-review.googlesource.com/c/1293431Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#602302}

third_party/blink/renderer/core/mojo/README.md

@@ -3,7 +3,7 @@ This document is a subset of the [Mojo documentation](/mojo/README.md).
 
 The JavaScript system API exposes the capabilities to create message pipes, data
 pipes, shared buffers and watchers. The API is defined using Web IDL. You could
-find the IDL files [here](https://cs.chromium.org/chromium/src/third_party/blink/Source/core/mojo/).
+find the IDL files [here](https://cs.chromium.org/chromium/src/third_party/blink/renderer/core/mojo/)
 
 Please refer to the low-level [C system API](/mojo/public/c/system/README.md)
 for more detailed documentation of equivalent methods.