Update git submodules

* Update external/autotest from branch 'master'
  to 18b42abae100177ded7f1e195f17b444487634c6
  - autotest: Allow single mouse scroll ticks of size 9 am: 101b5d0c24
    
    Original change: undetermined
    
    Change-Id: Ibc22be3fedc77fc19b2409b7fef5841a00ea6ea5
    
  - autotest: Allow single mouse scroll ticks of size 9
    
    BUG=chromium:1057812
    TEST=ran test locally
    
    Change-Id: I529061fa5e5338011bcb77c475fdc5c6bc489818
    Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/autotest/+/2337698
    Reviewed-by: Kalin Stoyanov <kalin@chromium.org>
    Tested-by: Sean O'Brien <seobrien@chromium.org>
    Commit-Queue: Sean O'Brien <seobrien@chromium.org>
    
diff --git a/external/autotest b/external/autotest
index 2696cd8..18b42ab 160000
--- a/external/autotest
+++ b/external/autotest
@@ -1 +1 @@
-Subproject commit 2696cd8183d713fd8fe3011ae4582f2ca191dc4f
+Subproject commit 18b42abae100177ded7f1e195f17b444487634c6