Fix linter warnings

[thomas-fossati]

Running linter on the package:

dice.go:18:1:warning: comment on exported type SubjectPublicKeyInfo should be of the form "SubjectPublicKeyInfo ..." (with optional leading article) (golint)
dice.go:40:6:warning: type name will be used as dice.DiceData by other packages, and that stutters; consider calling this Data (golint)
dice.go:46:6:warning: type name will be used as dice.DiceExtension by other packages, and that stutters; consider calling this Extension (golint)

For now, this has been handled via lint suppressions.