docs: fix spelling error. (#333)

Author: Paul Halliday

docs/en/api/config.md

@@ -22,5 +22,5 @@ Example:
 ```js
 import VueTestUtils from 'vue-test-utils'
 
-VueTestUtils.config.stubs['my-compomnent'] = '<div />'
+VueTestUtils.config.stubs['my-component'] = '<div />'
 ```