Build with Go 1.6

* Mention requiring Go 1.6+ in the README in preparation for a follow
   up PR which updates our docs / Makefile to align with our vendored
   dependencies.

Godeps/Godeps.json

@@ -1,6 +1,6 @@
 {
 	"ImportPath": "github.com/hashicorp/terraform",
-	"GoVersion": "go1.5",
+	"GoVersion": "go1.6",
 	"Packages": [
 		"./..."
 	],

README.md

@@ -29,7 +29,7 @@ All documentation is available on the [Terraform website](http://www.terraform.i
 Developing Terraform
 --------------------
 
-If you wish to work on Terraform itself or any of its built-in providers, you'll first need [Go](http://www.golang.org) installed on your machine (version 1.4+ is *required*). Alternatively, you can use the Vagrantfile in the root of this repo to stand up a virtual machine with the appropriate dev tooling already set up for you.
+If you wish to work on Terraform itself or any of its built-in providers, you'll first need [Go](http://www.golang.org) installed on your machine (version 1.6+ is *required*). Alternatively, you can use the Vagrantfile in the root of this repo to stand up a virtual machine with the appropriate dev tooling already set up for you.
 
 For local dev first make sure Go is properly installed, including setting up a [GOPATH](http://golang.org/doc/code.html#GOPATH). You will also need to add `$GOPATH/bin` to your `$PATH`. Next, install the following software packages, which are needed for some dependencies:
 

Vagrantfile

@@ -5,7 +5,7 @@
 VAGRANTFILE_API_VERSION = "2"
 
 $script = <<SCRIPT
-GOVERSION="1.5.1"
+GOVERSION="1.6"
 SRCROOT="/opt/go"
 SRCPATH="/opt/gopath"