Update golang:cross references

golang/content.md

@@ -13,7 +13,7 @@ Go (a.k.a., Golang) is a programming language first developed at Google. It is a
 The most straightforward way to use this image is to use a Go container as both the build and runtime environment. In your `Dockerfile`, writing something along the lines of the following will compile and run your project:
 
 ```dockerfile
-FROM golang:1.3-onbuild
+FROM golang:1.6-onbuild
 ```
 
 This image includes multiple `ONBUILD` triggers which should cover most applications. The build will `COPY . /go/src/app`, `RUN go get -d -v`, and `RUN go install -v`.
@@ -34,27 +34,27 @@ $ docker run -it --rm --name my-running-app my-golang-app
 There may be occasions where it is not appropriate to run your app inside a container. To compile, but not run your app inside the Docker instance, you can write something like:
 
 ```console
-$ docker run --rm -v "$PWD":/usr/src/myapp -w /usr/src/myapp golang:1.3 go build -v
+$ docker run --rm -v "$PWD":/usr/src/myapp -w /usr/src/myapp golang:1.6 go build -v
 ```
 
 This will add your current directory as a volume to the container, set the working directory to the volume, and run the command `go build` which will tell go to compile the project in the working directory and output the executable to `myapp`. Alternatively, if you have a `Makefile`, you can run the `make` command inside your container.
 
 ```console
-$ docker run --rm -v "$PWD":/usr/src/myapp -w /usr/src/myapp golang:1.3 bash -c make
+$ docker run --rm -v "$PWD":/usr/src/myapp -w /usr/src/myapp golang:1.6 bash -c make
 ```
 
 ## Cross-compile your app inside the Docker container
 
-If you need to compile your application for a platform other than `linux/amd64` (such as `windows/386`), this can be easily accomplished with the provided `cross` tags:
+If you need to compile your application for a platform other than `linux/amd64` (such as `windows/386`):
 
 ```console
-$ docker run --rm -v "$PWD":/usr/src/myapp -w /usr/src/myapp -e GOOS=windows -e GOARCH=386 golang:1.3-cross go build -v
+$ docker run --rm -v "$PWD":/usr/src/myapp -w /usr/src/myapp -e GOOS=windows -e GOARCH=386 golang:1.6 go build -v
 ```
 
 Alternatively, you can build for multiple platforms at once:
 
 ```console
-$ docker run --rm -it -v "$PWD":/usr/src/myapp -w /usr/src/myapp golang:1.3-cross bash
+$ docker run --rm -it -v "$PWD":/usr/src/myapp -w /usr/src/myapp golang:1.6 bash
 $ for GOOS in darwin linux; do
 >   for GOARCH in 386 amd64; do
 >     go build -v -o myapp-$GOOS-$GOARCH