Add missing "of" to testing guide.
|@@ -144,7 +144,7 @@ email(david.partner.email, david.location_tonight)|
|### Console Tasks for Running your Tests|
|Rails comes with a CLI command to run tests.|
|-Here are some examples how to use it:|
|+Here are some examples of how to use it:|
|$ bin/rails test # run all tests in the `test` directory|