Nimscript errors aren't shown
I've just realised that nimscript errors are hidden behind the ``--verbose`` flag:

```
~/.nimble/pkgs/nimble-0.9.0 » ~/projects/nimble/src/nimble check --verbose                                                             1 ↵
    Reading config file at /Users/dom/.config/nimble/nimble.ini
NimCompilerApiVersion @[]
    Setting Nim stdlib prefix to /Users/dom/projects/nim
    Setting Nim stdlib path to /Users/dom/projects/nim/lib
       Info Hint: used config file '/Users/dom/projects/nim/config/nim.cfg' [Conf]
       Info /Users/dom/projects/nim/lib/core/macros.nim(719, 15) Error: undeclared identifier: 'float128'
       Info /Users/dom/projects/nim/lib/core/macros.nim(1070, 49) template/generic instantiation of `$` from here
       Info /Users/dom/projects/nim/lib/system/dollars.nim(126, 21) template/generic instantiation of `collectionToString` from here
       Info /Users/dom/projects/nim/lib/system/dollars.nim(110, 67) Error: type mismatch
     Error: nimble.nim(1123)         nimble
        ... nimble.nim(1096)         doAction
        ... nimble.nim(1036)         check
        ... common.nim(51)           raiseNimbleError
        ... Could not validate package:
        ... Could not read package info file in /Users/dom/.nimble/pkgs/nimble-0.9.0/nimble.nimble;
        ...   Reading as ini file failed with: 
        ...     Invalid section: .
        ...   Evaluating as NimScript file failed with: 
        ...     /Users/dom/.nimble/pkgs/nimble-0.9.0/nimble.nimble(33, 1) Error: undeclared identifier: 'task'.
```

They should be shown as an error when "error" is in the message.