Fix location header

Author: francisco-videira-nhs

lambdas/api-handler/src/handlers/__tests__/get-letter-data.test.ts

@@ -47,7 +47,9 @@ describe('API Lambda handler', () => {
 
     expect(result).toEqual({
       statusCode: 303,
-      Location: 'https://somePreSignedUrl.com',
+      headers: {
+        'Location': 'https://somePreSignedUrl.com',
+      },
       body: ''
     });
   });

lambdas/api-handler/src/handlers/get-letter-data.ts

@@ -22,7 +22,9 @@ export const getLetterData: APIGatewayProxyHandler = async (event) => {
 
     return {
       statusCode: 303,
-      Location: await getLetterDataUrl(supplierId, letterId, letterRepo),
+      headers: {
+        'Location': await getLetterDataUrl(supplierId, letterId, letterRepo)
+      },
       body: ''
     };
   }