Fix swiftshader Dockerfile.

Change-Id: I2e7ecd5f6a6891c32b9a65931592b80e2d52afea
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/304004
Auto-Submit: Joe Gregorio <jcgregorio@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
1 file changed