traverse.clearCache is not a function

#### Input Code

```js
const foo = "foo";
const bar = `asdf ${foo} asd ${foo}`
```

[Babel REPL link](https://babeljs.io/repl#?babili=true&browsers=&build=&builtIns=false&code_lz=MYewdgzgLgBAZiEMC8MBECRoNwChSSwBGAhgE4owAGJAJiRLTACQDemAvjA0251UA&debug=false&forceAllTransforms=false&shippedProposals=false&circleciRepo=&evaluate=true&fileSize=false&lineWrap=false&presets=babili&prettier=false&targets=Node-8.7&version=7.0.0-beta.38&envVersion=)

#### Actual Output

```js
traverse.clearCache is not a function. (In 'traverse.clearCache()', 'traverse.clearCache' is undefined)
```

#### Expected Output

```js
const bar = `asdf foo asd foo`
```

#### Details

Noticed this bug when playing around on the repl. Only the `minify` plugin is enabled.

Start with the minimal input in the linked Babel REPL and reproduce the failure with only the minify plugin enabled. Trace where the REPL invokes minification and where traverse.clearCache is called; done means the input transforms to `const bar = \`asdf foo asd foo\`` without the error.

Written by the indexing model from the issue text.