Update dep installation in DEVELOPER_GUIDE (#194)
Update dep installation in DEVELOPER_GUIDE (#194)

`dep` installed via the install script gets the latest version of `dep`. If a contributor installs `dep` via `apt-get`, for example, they might push a dependency that would be removed if someone were running `dep` installed via the script: `dep` installed via `apt-get` ignores the [[prune]] section of Gopkg.toml while `dep` installed via the script does not. Also, `dep` via `apt-get` removes `pruneopts` etc (which are present when you run `dep` installed via the script), rewriting ~67% of Godep.lock, when someone tries to add a new dependency.
kubeflow/kfserving-lts,kubeflow/kfserving-lts,kubeflow/kfserving-lts,kubeflow/kfserving-lts,kubeflow/kfserving-lts,kubeflow/kfserving-lts