Allow the j shortcut in testUtils

Since the API allows the `j` shortcut, the mock test API should implement it as well.

Author: no23reason

src/testUtils.js

@@ -27,6 +27,7 @@ function applyTransform(module, options, input, testOptions = {}) {
     input,
     {
       jscodeshift,
+      j: jscodeshift,
       stats: () => {},
     },
     options || {}