docs: fix add for @vue/cli-plugin-unit-mocha (#1312)

MoYummy · yyx990803 · commit 23cf71314a45 · 2018-05-17T14:54:36.000-04:00
diff --git a/packages/@vue/cli-plugin-unit-mocha/README.md b/packages/@vue/cli-plugin-unit-mocha/README.md
@@ -31,5 +31,5 @@
 ## Installing in an Already Created Project
 
 ``` sh
-vue add unit-mocha
+vue add @vue/unit-mocha
 ```
