Fix docker build / make image: adding git to Dockerfile builder

[afarbos]

Today since git is not installed while building the docker image the version is not set, see below:

 ---> Running in e12300c7f495
CGO_ENABLED=0 go build -ldflags '-s -w -X main.version=' -o daytona cmd/daytona/main.go
make: git: No such file or directory

Adding git will allow to retrieve the version, and generate the image like:

 ---> Running in f6d8e64950e9
CGO_ENABLED=0 go build -ldflags '-s -w -X main.version=v1.1.2-1-g50f1ad1' -o daytona cmd/daytona/main.go

[dustin-decker]

Thank you