Bug 1593782 - Add period to policy. DONTBUILD r=fluent-reviewers,flod

Differential Revision: https://phabricator.services.mozilla.com/D52422

--HG--
extra : moz-landing-system : lando

browser/locales/en-US/browser/policies/policies-descriptions.ftl

@@ -107,7 +107,7 @@ policy-Homepage = Set and optionally lock the homepage.
 
 policy-InstallAddonsPermission = Allow certain websites to install add-ons.
 
-policy-LegacyProfiles = Disable the feature enforcing a separate profile for each installation
+policy-LegacyProfiles = Disable the feature enforcing a separate profile for each installation.
 
 policy-LocalFileLinks = Allow specific websites to link to local files.