Function declarations within blocks are transpiled into code that breaks on some pre-ES2015 targets

Prior to ES2015, function declarations within blocks were forbidden in strict mode (See [MDN web docs](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/block)):

```
(function() {
'use strict';
if (1) {
function x() {
// This results in "Strict mode does not allow function declarations in a
// lexically nested statement" or a similar error in some older browsers
}
}
})();
```

(Sorry, I didn't have the weapons to test this myself, just consulted the and trust my colleague's report.)

We ran into this issue when we saw some some buble-transformed code crash on iOS 9 Safari.

Would it be within Bublé's scope to transform this into equivalent code that works? E.g.:

```
(function() {
'use strict';
if (1) {
var x = function x() {
// Tada!
}
}
})();
```

Reproduce the strict-mode example on an affected pre-ES2015 target, then trace Bublé's handling of function declarations inside blocks. Compare the generated output with the issue's proposed equivalent and verify that it runs on iOS 9 Safari or a comparable older target without the reported syntax error.

Written by the indexing model from the issue text.