let declaration treated as var declaration

[adiba]

This should throw an error on execute if a is not defined outside the blocks.

{
    let a;
}
{
    a++;
}

However, escope treats both as as the same variable.
Tested with http://esprima.org/demo/rename.html

Related: #57

[0xdevalias]

See also:

• Add ES6 Support #33
• Try blocks not identified as scope level #57