How do I deal with upstairs neighbors nervous dog?

The neighbors that live above me just got a pit bull mix. My initial meeting with the dog went well and he allowed me to pet him. They keep him on a long line in the front yard during the day. I get home from work and pull into the garage. He then starts barking at me in a nervous, territorial feeling bark. I’ve let him come up to me and sniff my hand. After sniffing my hand, he resumes barking again, even closer now. When I try to go past him to my front door, he cuts off my path and resumes barking. How can I overcome his nervousness around me and feel comfortable walking to my front door again?