Change: Remove Jest 27 version specification

Closes #406 
Specifying the version number makes the installation fail. 
Omitting the version number results in installing the correct alpha version.

Author: awulkan

README.md

@@ -10,12 +10,12 @@ Since we need to support a variety of Vue and Jest versions, vue-jest doesn't fo
 | ----------- | ----------------- | ------------------- |
 | Vue 2       | Jest 26 and below | `vue-jest@4`        |
 | Vue 3       | Jest 26 and below | `vue-jest@5`        |
-| Vue 2       | Jest 27           | `@vue/vue2-jest@27` |
-| Vue 3       | Jest 27           | `@vue/vue3-jest@27` |
+| Vue 2       | Jest 27           | `@vue/vue2-jest`    |
+| Vue 3       | Jest 27           | `@vue/vue3-jest`    |
 
 ```bash
-npm install --save-dev @vue/vue2-jest@27 # (use the appropriate version)
-yarn add @vue/vue2-jest@27 --dev
+npm install --save-dev @vue/vue2-jest
+yarn add @vue/vue2-jest --dev
 ```
 
 ## Setup