Allow @import RegEx to find all Import Types

[JanThiel]

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Added missing Import directives to RegEx:

• once
• reference
• multiple
• inline

getImports should now also return

@import (reference) file.less @import (multiple) file.less @import (once) file.less @import (inline) file.less

fixes #60

[JanThiel]

I missed to extend the importType check in .resolveImports(). This is fixed so the imports are recognized correctly.