Update to last core-retrieval version on Glide

[ajnavarro]

No description provided.

[bzz]

Not sure what is the proposed test plan for this changes, but I tried make and that's the result

make                                                                                  
Makefile:40: warning: overriding commands for target `test'
Makefile.main:149: warning: ignoring old commands for target `test'
Makefile:43: warning: overriding commands for target `test-coverage'
Makefile.main:152: warning: ignoring old commands for target `test-coverage'
make: `Makefile.main' is up to date.

I tried following instructions https://github.com/src-d/borges#build and got

 make packages                                                                         
Makefile:40: warning: overriding commands for target `test'
Makefile.main:149: warning: ignoring old commands for target `test'
Makefile:43: warning: overriding commands for target `test-coverage'
Makefile.main:152: warning: ignoring old commands for target `test-coverage'
consumer.go:6:2: cannot find package "gopkg.in/src-d/core-retrieval.v0" in any of:
	/usr/local/Cellar/go/1.8.1/libexec/src/gopkg.in/src-d/core-retrieval.v0 (from $GOROOT)
	/Users/alex/go/src/gopkg.in/src-d/core-retrieval.v0 (from $GOPATH)
../../mentionjobiter.go:4:2: cannot find package "gopkg.in/src-d/core-retrieval.v0/model" in any of:
	/usr/local/Cellar/go/1.8.1/libexec/src/gopkg.in/src-d/core-retrieval.v0/model (from $GOROOT)
	/Users/alex/go/src/gopkg.in/src-d/core-retrieval.v0/model (from $GOPATH)
../../archiver.go:11:2: cannot find package "gopkg.in/src-d/core-retrieval.v0/repository" in any of:
	/usr/local/Cellar/go/1.8.1/libexec/src/gopkg.in/src-d/core-retrieval.v0/repository (from $GOROOT)
	/Users/alex/go/src/gopkg.in/src-d/core-retrieval.v0/repository (from $GOPATH)
../../common.go:10:2: cannot find package "gopkg.in/src-d/core.v0" in any of:
	/usr/local/Cellar/go/1.8.1/libexec/src/gopkg.in/src-d/core.v0 (from $GOROOT)

Am I missing something, or our dev section of the doc should be updated?

@ajnavarro I know that it might be not related to this change per-se, but do you think it might be worth taking care of it in this PR?

[bzz]

It seems that instructions in docs are right and #70 takes care of this issue. So let's may be rebase as soon as it's merged?

[bzz]

Tested locally, looks great 👍

Let's merge the guy?