Omitting semicolon from `import` causes the following line to be truncated

This PR adds a failing test for compiling input with semicolons omitted. I'm not quite sure how to fix the underlying issue, though.

When using semicolons, a whole import statement is parsed as `import { $ } from 'jquery';`. When omitting them, however, the import statement is parsed as `import { $ } from 'jquery'\n`.

[source_modifier.js#L32](https://github.com/square/es6-module-transpiler/blob/master/lib/source_modifier.js#L32) skips the next character after the end of the replaced range. This is typically a newline, but in the cases below it is actually the first character of the next statement.

**Input:**
```js
import $ from "jquery"
console.log('foo')
// Or
import $ from "jquery";console.log('foo')
```
**Output:**
```js
define("application", 
  ["jquery"],
  function(__dependency1__) {
    "use strict";
    var $ = __dependency1__['default'];
    onsole.log('foo') // Missing first character
    ;
  });
```