When fetching packages with go get, remove redundant go install

[bradleyfalzon]

"go get" fetches and installs the specified package according to the
documentation:

Get downloads the packages named by the import paths, along with their
dependencies. It then installs the named packages, like 'go install'.

Testing this myself on go1.8.3 and go1.9rc2 having an older version of
buffalo binary install, then running:

go get -u github.com/gobuffalo/buffalo/...

Shows the binary is also updated successfully when checking the version.

Relates to documentation update: gobuffalo/docs#57

Further, this appears to have first started with 1bcb981#diff-00e5b9d3695f2772e4d4422b4fee4787R92 where there's a glide get of github.com/markbates/refresh followed by go install of the same package. Could this have initially been a glide vs go behaviour difference that continued through the various refactors? But it seems safe to remove the additional go install now.

I have tested this on a basic buffalo new <name>, but I haven't extensively tested this change in regards to the soda related changes or Dockerfile.

[markbates]

Can you please change the base for this PR to the development branch? Thank you.

[markbates]

This is needed. We run our tests using this dockerfile so we want to make sure we are running the tests using the code that was just committed.

[bradleyfalzon]

Sure, but are you certain it's needed? The go get should be handling this. But I can add it back, no issue.

[bradleyfalzon]

Definitely needed. It's compiling the local source.

OK, but I've tested by adding a panic to new generator and the buffalo new commands started to panic. The go get should still install the local version.

But I'll add it back now.

[markbates]

Definitely needed. It's compiling the local source.

[bradleyfalzon]

I've changed the base branch and removed the Dockerfile modifications, ready for a second review.

[markbates]

Thanks!