The BuildKit dockerignore package was integrated in the patternmatcher
repository / module. This patch updates our uses of the BuildKit package
with its new location.
A small local change was made to keep the format of the existing error message,
because the "ignorefile" package is slightly more agnostic in that respect
and doesn't include ".dockerignore" in the error message.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
