deps: update c-ares to 1.18.1

Updated as described in doc/guides/maintaining-c-ares.md.

PR-URL: #40660
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: Tobias Nießen <[email protected]>
Reviewed-By: Michaël Zasso <[email protected]>

Author: richardlau

deps/cares/CHANGES

@@ -0,0 +1,15 @@
+Contributing to c-ares
+======================
+
+To contribute patches to c-ares, please generate a GitHub pull request
+and follow these guidelines:
+
+ - Check that the Travis builds are green for your pull request.
+ - Please update the test suite to add a test case for any new functionality.
+ - Build the library with `./configure --enable-debug --enable-maintainer-mode` and
+   ensure there are no new warnings.
+
+To improve the chances of the c-ares maintainers responding to your request:
+
+ - Also send an email to the mailing list at `[email protected]` describing your change.
+ - To follow any associated discussion, please subscribe to the [mailing list](http://lists.haxx.se/listinfo/c-ares).