Introduce an internal package, internal/version to hold the Go version
constant. This probably won't matter after 0.5 drops support for Go 1.7
and earlier, but this refactoring makes it clear that the constant is
defined in one place, so we can delete it in one place.
Introduce an internal package, internal/version to hold the Go version constant. This probably won't matter after 0.5 drops support for Go 1.7 and earlier, but this refactoring makes it clear that the constant is defined in one place, so we can delete it in one place.