fix for varid bug in showExports & processExports

```shell
ghc-mod browse -o Control.Lens.Prism
(_Just)
(_Left)
(_Nothing)
(_Right)
(_Show)
(_Void)
APrism
```
Haskell 2010:
```
small -> ascSmall | uniSmall | _
ascSmall -> a | b | ... | z
uniSmall -> any Unicode lowercase letter
varid -> (small {small | large | digit | ' })
```