fix: compatability with verbatimModuleSyntax

[LoaderB0T]

Fixes: #114

This PR extends the Dependency class & text generator to generate the import statement with the "type" keyword when the imported symbol is a type or interface.

This required typescript 3.8 or later, so this might be a breaking change.

EDIT:

I also had to update the prettier version because the old version did not know the "type" keyword in that context.