Output code is invalid when input is { [a]: function*(){ } }

**Input.js**
```
let a = 1 ;

let obj = {
	[a]: function*(){ }
} ;
```

**Command line:**
```
java -jar closure-compiler-v20190121.jar --language_out NO_TRANSPILE -O SIMPLE  --js_output_file Output.js Input.js
```
**Output.js**
```
'use strict';
let a = 1, obj = {*[a]:function*() {
}};
```

Output file contains invalid syntax. There's an extra asterisk before `[a]`.