direct-to-sd doesn't build

[josephburnett]

When trying to modify and docker build the custom metrics autoscaling direct to Stackdriver example, the build fails with no buildable Go source files in /go/src/google.golang.org/api/transport/http/internal/propagation

$ docker build -t direct-to-sd .
Sending build context to Docker daemon  12.29kB
Step 1/9 : FROM golang:1.7.3
 ---> ef15416724f6
Step 2/9 : ADD . /go/src/direct-to-sd
 ---> Using cache
 ---> 425ccb5c64d0
Step 3/9 : RUN go get cloud.google.com/go/compute/metadata
 ---> Using cache
 ---> 4e85f56c9172
Step 4/9 : RUN go get golang.org/x/oauth2
 ---> Using cache
 ---> 0651c69fb6f1
Step 5/9 : RUN go get google.golang.org/api/monitoring/v3
 ---> Running in 896d9b622d40
src/google.golang.org/api/transport/http/dial.go:30:2: no buildable Go source files in /go/src/google.golang.org/api/transport/http/internal/propagation
The command '/bin/sh -c go get google.golang.org/api/monitoring/v3' returned a non-zero code: 1