Dockerfile: update Go version to 1.10

Fixes golang/go#24022

Change-Id: I76177ad853c19d80627ec7490c48c73c4e4b0fc7
Reviewed-on: https://go-review.googlesource.com/96197
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/Dockerfile b/Dockerfile
index a1ca757..ddec475 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -7,7 +7,7 @@
 ENV GOPATH /go
 ENV PATH /usr/local/go/bin:$GOPATH/bin:$PATH
 ENV GOROOT_BOOTSTRAP /usr/local/gobootstrap
-ENV GO_VERSION 1.9.3
+ENV GO_VERSION 1.10
 ENV DEPS 'ca-certificates'
 ENV BUILD_DEPS 'curl bzip2 git gcc patch libc6-dev'