Add back <strong> tag in HTML revert notification email

Change I0243d290a updated the wording of the email, and at the same
time removed the <strong> tag. This makes the formatting of the mail
inconsistent with others, which still have <strong>.

Add it back.

Bug: Issue 8731
Change-Id: I8fe6202f7a7f9687928e35be3b5b80fd093653f2
diff --git a/gerrit-server/src/main/resources/com/google/gerrit/server/mail/RevertedHtml.soy b/gerrit-server/src/main/resources/com/google/gerrit/server/mail/RevertedHtml.soy
index 52c00ec..ff3cf24 100644
--- a/gerrit-server/src/main/resources/com/google/gerrit/server/mail/RevertedHtml.soy
+++ b/gerrit-server/src/main/resources/com/google/gerrit/server/mail/RevertedHtml.soy
@@ -22,7 +22,7 @@
  */
 {template .RevertedHtml autoescape="strict" kind="html"}
   <p>
-    {$fromName} has created a revert of this change.
+    {$fromName} has <strong>created a revert</strong> of this change.
   </p>
 
   {if $email.changeUrl}