Merge pull request #420 from tonistiigi/1903-buildkit-update

[19.03] vendor: update buildkit to ff93519ee
Upstream-commit: 5d5083a57a1c071a935bc6a1be6b1b1cc5cf1ede
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                            ae10b292fefb00e0fbf9fecd1419c5f252e58895
+github.com/moby/buildkit                            ff93519eefb7d4b2ee67dd78166cd5d0f52f8980
 github.com/tonistiigi/fsutil                        3d2716dd0a4d06ff854241c7e8b6f3f904e1719f
 github.com/grpc-ecosystem/grpc-opentracing          8e809c8a86450a29b90dcc9efbf062d0fe6d9746
 github.com/opentracing/opentracing-go               1361b9cd60be79c4c3a7fa9841b3c132e40066a7