Don't merge test options. (#6157)

* Don't merge test options.

Particularly, I don't want `lodash/merge` to merge my specific plugins
with the general test plugins. It led to odd behavior where I could
enable a loose transform in my specific test, just to have it overridden
by the test fixture's general options.

* Need options

packages/babel-plugin-transform-es2015-classes/test/fixtures/spec/super-reference-before-in-lambda/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["external-helpers", "transform-es2015-classes", "transform-es2015-block-scoping"]
+}