Fix grammar

wiki/src/support/known_issues.mdwn

@@ -495,11 +495,11 @@ Tails fails to start or behaves weirdly after an automatic upgrade
 
 Sometimes, after an automatic upgrade, your Tails might either:
 
-- Fails to start. Often after the message:
+- Fail to start. Often after the message:
 
   <pre>Loading, please wait...</pre>
 
-- Behaves weirdly. For example, your keyboard does not work or you cannot
+- Behave weirdly. For example, your keyboard does not work or you cannot
   connect to a network.
 
 To fix this problem, you can [[update your Tails