Markdown to HTML conversion issue with newline.

```
const input = "testing *1 line* italics\n\ntesting **2 line bold **test\n\ntesting 3 line \n\nunderline "
```

```
const c = new showdown.Converter({simpleLineBreaks: true})
const output = c.makeHtml(input);
```

```
testing 1 line italics\ntesting **2 line bold **test\ntesting 3 line \nunderline 
```

Here 2 line bold is not wrapped with strong tag