title: Can't `go get` dependencies during docker build
body: <p>I'm fairly new to both Docker and go, so this might be something obvious, but my google searches haven't found anything.</p>
  
  <p>I'm trying to build a simple go program with docker, but I'm havign trouble with dependencies.</p>
  
  <p>go file:</p>
  
  <pre><code>package main
  
  import (
      "fmt"
      "log"
      "html"
      "net/http"
  
      "github.com/gorilla/mux"
  )
  
  func hello(writer http.ResponseWriter, r *http.Request) {
      path := mux.Vars(r)["rest"]
      fmt.Fprintf(writer, "Hello, %q", html.EscapeString(path))
  }
  
  func main() {
      router := mux.NewRouter().StrictSlash(true)
  
      router.HandleFunc("/{rest:.*}", hello)
  
      log.Println("Listening...")
      log.Fatal(http.ListenAndServe(":8080", router))
  }
  </code></pre>
  
  <p>Docker file:</p>
  
  <pre><code>FROM golang:latest
  RUN mkdir /app
  ADD ./HelloWorld.go /app/
  WORKDIR /app
  RUN go get ./*.go
  RUN go build -o main .
  CMD ["/app/main"]
  </code></pre>
  
  <p>Error:</p>
  
  <pre><code>Sending build context to Docker daemon  6.482MB
  Step 1/7 : FROM golang:latest
   ---&gt; 138bd936fa29
  ...
  Step 5/7 : RUN go get ./*.go
   ---&gt; Running in 1e29844961a2
  HelloWorld.go:9:5: cannot find package "github.com/gorilla/mux" in any of:
          /usr/local/go/src/github.com/gorilla/mux (from $GOROOT)
          /go/src/github.com/gorilla/mux (from $GOPATH)
  The command '/bin/sh -c go get ./*.go' returned a non-zero code: 1
  </code></pre>