uppercase header to mimic docker CLI behavior
uppercase header to mimic docker CLI behavior

jesper/crane,tmc/crane,t-suwa/crane,bjaglin/crane,dreamcat4/crane,stajkowski/crane,dreamcat4/crane,michaelsauter/crane,inthroxify/crane,rmoorman/crane,rmoorman/crane,jesper/crane,bjaglin/crane,t-suwa/crane,inthroxify/crane,michaelsauter/crane,tmc/crane,stajkowski/crane