Merge pull request #40955 from tonistiigi/19.03-buildkit-update

[19.03] vendor: update buildkit to a7d7b7f1
Upstream-commit: ab567a4327f8a46d2fc7b5b11d626d4ea8129cca
Component: engine

Author: AkihiroSuda

components/engine/vendor.conf

@@ -26,7 +26,7 @@ github.com/imdario/mergo                            7c29201646fa3de8506f70121347
 golang.org/x/sync                                   e225da77a7e68af35c70ccbf71af2b83e6acac3c
 
 # buildkit
-github.com/moby/buildkit                            59e305aa33fd96e51d5c458f55104250b3e39f56 # v0.6.4-5-g59e305aa
+github.com/moby/buildkit                            a7d7b7f1e6bfc102810079f13212de6a869c494b # v0.6.4-11-ga7d7b7f1
 github.com/tonistiigi/fsutil                        6c909ab392c173a4264ae1bfcbc0450b9aac0c7d
 github.com/grpc-ecosystem/grpc-opentracing          8e809c8a86450a29b90dcc9efbf062d0fe6d9746
 github.com/opentracing/opentracing-go               1361b9cd60be79c4c3a7fa9841b3c132e40066a7