minor symfony#9274 Typo fix (toniperic)

This PR was submitted for the 3.3 branch but it was merged into the 2.8 branch instead (closes symfony#9274).

Discussion
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Typo fix

Commits
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fba5578 Typo fix

Author: javiereguiluz

security/guard_authentication.rst

@@ -419,7 +419,7 @@ Each authenticator needs the following methods:
 
 **supportsRememberMe()**
     If you want to support "remember me" functionality, return true from this method.
-    You will still need to active ``remember_me`` under your firewall for it to work.
+    You will still need to activate ``remember_me`` under your firewall for it to work.
     Since this is a stateless API, you do not want to support "remember me"
     functionality in this example.