For an elephant that can fly, Dumbo sure is having a hard time getting off the ground. Tim Burton's live-action reboot—or "reimagining" if you're nasty—officially nabbed $45 million in its debut weekend, flying below the $50 million mark that early predictions pointed to. This isn't anywhere close to a home run, especially for a Disney project. Dumbo now sits toward the bottom of the Disney live-action bracket, beating out the openings of Pete's Dragon ($21.5 million) and Alice Through the Looking Glass ($26 million), but well below the loftier numbers of …