Incorrect code with jQuery functionality

A function defined in jQuery sections is incorrectly optimized

**To Reproduce**

Minimal code to reproduce the bug

```
(function($) {
Math.gcd = function(x, y) {
return y === 0 ? x : Math.gcd(y, x % y);
};
})(typeof jQuery !== 'undefined' ? jQuery : {});

$(document).ready(function() {
var test = Math.gcd(170, 150);
console.log(test);
});
```

**Actual Output**

If there is no Error thrown,

```
(function() {
var a=Math.gcd;
a=function(b,c) {
return 0===c ? b : a (c,b%c)
}
}) ("undefined"==typeof jQuery ? { } : jQuery)

$(document).ready(function() {
var a=Math.gcd(170,150);
console.log(a)
}
);
```

**Expected Output**

```
(function($) {
Math.gcd=function(b,c) {
return 0===c ? b : Math.gcd(c,b%c)
}
}) ("undefined"==typeof jQuery ? { } : jQuery)

$(document).ready(function() {
var a=Math.gcd(170,150);
console.log(a)
}
);
```
**Configuration**

How are you using babel-minify?

`babel-minify CLI`

babel-minify version: `0.4.3`

babel version : `7.0.0-beta.46`

babel-minify-config:

Default

Reproduce the supplied snippet with the babel-minify CLI using babel-minify 0.4.3 and Babel 7.0.0-beta.46, then trace the optimization that changes the jQuery-wrapped Math.gcd definition. Done means the minified output preserves the expected Math.gcd behavior and the reproduction is covered by an appropriate regression test.

Written by the indexing model from the issue text.