Fix coverage flag for test command

Signed-off-by: Johannes M. Scheuermann <[email protected]>

docs/book/how-do-i-test-policies.md

@@ -221,7 +221,7 @@ If we run the coverage report on the original **example.rego** file without
 that line 8 is not covered.
 
 ```bash
-opa test --cover --format=json example.rego example_test.rego
+opa test --coverage --format=json example.rego example_test.rego
 ```
 
 ```json
@@ -488,4 +488,4 @@ The order of the criteria on the command line determine their priority.
 Another way to get the same output as above would be the following:
 ```bash
 opa eval --data rbac.rego --profile-limit 5 --profile-sort num_eval --profile-sort num_redo --format=pretty 'data.rbac.allow'
-```
+```