Haskell: illegal Happy file if category names use apostrophe

```
Prg_ . Prg' ::= "prg" ;
```
Happy does not like the grammar BNFC creates for it:
```haskell
Prg' :: { Prg' }
Prg' : 'prg' { Test.Abs.Prg_ }
```
```
Test/Par.y: Parse error
```
According to the Happy specification, identifiers for non-terminals may not use the apostrophe character:
https://www.haskell.org/happy/doc/html/sec-grammar-files.html#sec-lexical-rules