Allow single quoted attributes

Should work fine now.
Why doing this replace here and not inside the grammar itself such as line 224 in `hsp/compiler/parser/hspblocks.pegjs`

```
HTMLAttributeQuoted
    = '"' value:(HTMLAttributeTextDoubleQuoted / ExpressionTextBlock)* '"'
        {return value.replace(/"/g, "\\\"");}
    / "'" value:(HTMLAttributeTextSingleQuoted / ExpressionTextBlock)* "'"
        {return value.replace(/'/g, "\\\'");}
```