Build error when label's key in Dockerfile has quotes

[belaaiza]

Describe the bug
Building an image which the Dockerfile has the following labels:

LABEL "Author"="Some Value"
LABEL "Service"="sboot-app-name"

Error message:

ERROR failed to create build plan: failed to get dockerfile: failed to parse dockerfile: failed to create new directive (line 2): invalid character in variable key: "

To Reproduce
makisu build with a Dockerfile containing quotes on label key

Expected behavior
As at docker docs quotes are valid in label keys, I expect that the image is built correctly.