change names "raven" in help text of binary

[ecthiender]

Running graphql-engine -- --help outputs:

raven - Hasura's datastore

Usage: graphql-engine [--host HOST] [-p|--port PORT] [-u|--user USER]
                      [-p|--password PASSWORD] [--database-url DATABASE-URL]
                      [-d|--dbname NAME] COMMAND

Available options:
  -h,--help                Show this help text
  --host HOST              Postgres server host
  -p,--port PORT           Postgres server port
  -u,--user USER           Database user name
  -p,--password PASSWORD   Password of the user
  --database-url DATABASE-URL
                           Postgres database URL. Example
                           postgres://foo:bar@example.com:2345/database
  -d,--dbname NAME         Database name to connect to

Available commands:
  serve                    Start the HTTP api server
  export                   Export raven's schema to stdout
  clean                    Clean raven's metadata to start afresh
  execute                  Execute a query