Syntax Error with object spread

## test.js
```js
const a = { ...{ a: 1 } }
```

## bundle command
```bash
browserify -p bundle-collapser/plugin test.js
```

## output
```
SyntaxError: Unexpected token (1:12)
at Parser.pp$4.raise (./node_modules/acorn/dist/acorn.js:2840:15)
at Parser.pp.unexpected (/User./acorn/dist/acorn.js:689:10)
at Parser.pp$3.parseIdent (./node_modules/acorn/dist/acorn.js:2791:12)
at Parser.pp$3.parsePropertyName (./node_modules/acorn/dist/acorn.js:2597:107)
at Parser.pp$3.parseProperty (./node_modules/acorn/dist/acorn.js:2524:10)
at Parser.pp$3.parseObj (./node_modules/acorn/dist/acorn.js:2478:23)
at Parser.pp$3.parseExprAtom (./node_modules/acorn/dist/acorn.js:2239:19)
at Parser.pp$3.parseExprSubscripts (./node_modules/acorn/dist/acorn.js:2092:21)
at Parser.pp$3.parseMaybeUnary (./node_modules/acorn/dist/acorn.js:2069:19)
at Parser.pp$3.parseExprOps (./node_modules/acorn/dist/acorn.js:2013:21)
```

Browserify-Version: 16.5.1
Bundle-Collapser-Version: 1.4.0
Acorn-Version: 7.3.1