Formal specification link incorrect

[gwicksted]

In the readme, there is a "Formal specification of Zish" that points to https://github.com/tlocke/zish/blob/master/zish/Zish.g4 which gives a 404.

The correct link appears to be https://github.com/tlocke/zish/blob/master/Zish.g4 (remove the zish subdirectory)

[tlocke]

Thanks @gwicksted, this should be fixed now by e5a7c37.