fix parsing trailing quotes in backticked identifiers (#1408)

[ulysses4ever]

I assume this needs a test… It works on the example in #1408 provided by @Kleidukos

module Module where

-- | This is the `foo'` function.
foo' :: ()
foo' = ()

[Kleidukos]

@ulysses4ever This is wonderful! :)
Yes a test would be most welcome.

[ulysses4ever]

@Kleidukos done. Tests pass on my end.