Adding a "in" keyword in JWT's post route example. (#1065)

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There was a "in" keyword missing in the post route example for signing
JWTs. The keyword was simply added to the code snippet.
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Co-authored-by: Tim Condon <0xTim@users.noreply.github.com>

docs/security/jwt.es.md

@@ -94,7 +94,7 @@ struct TestPayload: JWTPayload {
 La firma de la carga útil se realiza llamando al método `sign` en el módulo `JWT`, por ejemplo dentro de un manejador de ruta:
 
 ```swift
-app.post("login") { req async throws -> [String: String]
+app.post("login") { req async throws -> [String: String] in
     let payload = TestPayload(
         subject: "vapor",
         expiration: .init(value: .distantFuture),

docs/security/jwt.md

@@ -93,7 +93,7 @@ struct TestPayload: JWTPayload {
 Signing the payload is done by calling the `sign` method on the `JWT` module, for example inside of a route handler:
 
 ```swift
-app.post("login") { req async throws -> [String: String]
+app.post("login") { req async throws -> [String: String] in
     let payload = TestPayload(
         subject: "vapor",
         expiration: .init(value: .distantFuture),