[wpt] Fix for invalid test

The author meant "reverse linear", not "reverse-linear"

Bug: 849152
Change-Id: I8273c0c5866ceebe5a150cd8e29a0a4047c7b813
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1881890
Auto-Submit: Aleks Totic <atotic@chromium.org>
Reviewed-by: David Grogan <dgrogan@chromium.org>
Commit-Queue: Aleks Totic <atotic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709686}

third_party/blink/web_tests/external/wpt/css/css-ui/outline-018-expected.txt

-This is a testharness.js-based test.
-FAIL outline-style is animated as a discrete type assert_equals: expected "dotted" but got "solid"
-Harness: the test ran to completion.
-

third_party/blink/web_tests/external/wpt/css/css-ui/outline-018.html

@@ -29,7 +29,7 @@
   outline: solid 1px black;
 }
 #test4 {
-  animation: outline-anim 3s 0s paused reverse-linear;
+  animation: outline-anim 3s 0s paused reverse linear;
   outline: solid 1px black;
 }
 </style>