docs: update stub component (#612)

Author: 38elements

Diff for: docs/en/api/config.md

@@ -15,7 +15,7 @@ Vue Test Utils includes a config object to defined options used by Vue Test Util
 The stub stored in `config.stubs` is used by default.  
 Stubs to use in components. These are overwritten by `stubs` passed in the mounting options.
 
-When passing `stubs` as an array in the mounting options, `config.stubs` are converted to an array, and will stub components with a basic component that returns `<!---->`.
+When passing `stubs` as an array in the mounting options, `config.stubs` are converted to an array, and will stub components with a basic component that returns `<${component name}-stub>`.
 
 Example:
 

Diff for: docs/en/api/options.md

@@ -99,7 +99,7 @@ expect(wrapper.find('#fooWrapper').html()).toBe('<div id="fooWrapper"><p>0,text1
 
 - type: `{ [name: string]: Component | boolean } | Array<string>`
 
-Stubs child components. Can be an Array of component names to stub, or an object. If `stubs` is an Array, every stub is `<!---->`.
+Stubs child components. Can be an Array of component names to stub, or an object. If `stubs` is an Array, every stub is `<${component name}-stub>`.
 
 Example: