minor #5964 Missing n in Column (joshuataylor)

This PR was submitted for the 3.0 branch but it was merged into the 2.8 branch instead (closes #5964).

Discussion
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Missing n in Column

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.8, 3.0, 3.1

Commits
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bc2447d Missing n in Column

cookbook/security/guard-authentication.rst

@@ -44,7 +44,7 @@ property they use to access their account via the API::
         private $username;
 
         /**
-         * @ORM\Colum(type"string", unique=true)
+         * @ORM\Column(type"string", unique=true)
          */
         private $apiKey;