Add empty .babelrc for CLI tests.

packages/babel-cli/test/.babelrc

@@ -1 +0,0 @@
-{}

packages/babel-cli/test/index.js

@@ -1,5 +1,3 @@
-"use strict";
-
 const includes = require("lodash/includes");
 const readdir = require("fs-readdir-recursive");
 const helper = require("babel-helper-fixtures");
@@ -40,6 +38,9 @@ const readDir = function (loc, filter) {
 };
 
 const saveInFiles = function (files) {
+  // Place an empty .babelrc in each test so tests won't unexpectedly get to repo-level config.
+  outputFileSync(".babelrc", "{}");
+
   Object.keys(files).forEach(function (filename) {
     const content = files[filename];
     outputFileSync(filename, content);