Remove unconditional calls to get_latest_version (#907)

[beckjake]

I'm pretty sure that it really is this easy.

[drewbanin]

Beautiful. LGTM when the tests pass

[beckjake]

@drewbanin ok, this is actually fixed now, you can see the tricky bit...

[drewbanin]

@beckjake I just tried running this locally and saw:

$ dbt --version
usage: dbt: data build tool [-h] [--version] [-d] [-S]
                            {init,clean,debug,deps,archive,run,compile,docs,seed,test}
                            ...
dbt: data build tool: error: too few arguments

[beckjake]

@drewbanin that's really weird, on my machine I get:

$ dbt --version
installed version: 0.11.0-a1
   latest version: 0.10.2

Your version of dbt is ahead of the latest release!

[drewbanin]

LGTM (again) when the tests pass!