Makefile: roll gox into updatedeps

No need to have an extra dev bootstrapping step when we can automate it!

Makefile

@@ -27,6 +27,7 @@ updatedeps:
 	$(eval REF := $(shell sh -c "\
 		git symbolic-ref --short HEAD 2>/dev/null \
 		|| git rev-parse HEAD"))
+	go get -u github.com/mitchellh/gox
 	go get -u golang.org/x/tools/cmd/stringer
 	go get -u golang.org/x/tools/cmd/vet
 	go get -f -u -v ./...

README.md

@@ -36,12 +36,6 @@ For local dev first make sure Go is properly installed, including setting up a [
 -	[Git](http://git-scm.com/)
 -	[Mercurial](http://mercurial.selenic.com/)
 
-Then, install [Gox](https://github.com/mitchellh/gox), which is used as a compilation tool on top of Go:
-
-```sh
-$ go get -u github.com/mitchellh/gox
-```
-
 Next, clone this repository into `$GOPATH/src/github.com/hashicorp/terraform`. Install the necessary dependencies by running `make updatedeps` and then just type `make`. This will compile some more dependencies and then run the tests. If this exits with exit status 0, then everything is working!
 
 ```sh