Merge pull request #422 from tonistiigi/1903-update-buildkit

[19.03] vendor: update buildkit to 928f3b48
Upstream-commit: ea84732a77251e0d7af278e2b7df1d6a59fca46b
Component: engine

Author: andrewhsu

components/engine/vendor.conf

@@ -26,7 +26,7 @@ github.com/imdario/mergo                            7c29201646fa3de8506f70121347
 golang.org/x/sync                                   e225da77a7e68af35c70ccbf71af2b83e6acac3c
 
 # buildkit
-github.com/moby/buildkit                            ff93519eefb7d4b2ee67dd78166cd5d0f52f8980
+github.com/moby/buildkit                            928f3b480d7460aacb401f68610058ffdb549aca
 github.com/tonistiigi/fsutil                        3d2716dd0a4d06ff854241c7e8b6f3f904e1719f
 github.com/grpc-ecosystem/grpc-opentracing          8e809c8a86450a29b90dcc9efbf062d0fe6d9746
 github.com/opentracing/opentracing-go               1361b9cd60be79c4c3a7fa9841b3c132e40066a7