ChromeOS: Correct the case of MinFilelistKB.

BUG=chromium:1014871

Change-Id: I76375fadefee910ed7274f984c91d46dc499fe0d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2002834
Auto-Submit: Brian Geffon <bgeffon@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: Brian Geffon <bgeffon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#732968}

testing/variations/fieldtrial_testing_config.json

@@ -1872,7 +1872,7 @@
             ]
         }
     ],
-    "CrOSMinFilelistKb": [
+    "CrOSMinFilelistKB": [
         {
             "platforms": [
                 "chromeos"