Fix typo: then -> than.

RELNOTES: None.
PiperOrigin-RevId: 214005326

site/docs/user-manual.html

diff --git a/site/docs/user-manual.html b/site/docs/user-manual.html
index f7dcecc..48a51ea 100644
--- a/site/docs/user-manual.html
+++ b/site/docs/user-manual.html
@@ -2716,7 +2716,7 @@
 <h4 id="flag--test_verbose_timeout_warnings"><code class='flag'>--test_verbose_timeout_warnings</code></h4>
 <p>
   This option tells Bazel to explicitly warn the user if a test's timeout is
-significantly longer then the test's actual execution time.  While a test's
+significantly longer than the test's actual execution time.  While a test's
 timeout should be set such that it is not flaky, a test that has a highly
 over-generous timeout can hide real problems that crop up unexpectedly.
 </p>