fixing the rootblock.json download path

[vishalchangrani]

operator ran into this error-

flow@flow--testnetv2--consensus-2:~/testnetv2/bin$ boot-tools/transit pull-root-block -t consensus-test -b /home/flow/bootstrap
INF downloading root block
INF downloading root block file from transit servers dest=/home/flow/bootstrap/public-root-information/root-block.json source=public-root-information/root-block.json
FTL could not download google bucket file error="error creating GCS object reader: storage: object doesn't exist"

The source source=public-root-information/root-block.json is incorrect and does not mention the bucket name