unix: update Dockerfile to Go 1.11

Change-Id: I934702b11d21434d9c6646228b05396d2aef1820
Reviewed-on: https://go-review.googlesource.com/132215
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/linux/Dockerfile

@@ -17,9 +17,9 @@ RUN git clone --branch v4.18 --depth 1 https://kernel.googlesource.com/pub/scm/l
 RUN git clone --branch glibc-2.28 --depth 1 git://sourceware.org/git/glibc.git
 
 # Get Go
-ENV GOLANG_VERSION 1.11beta3
+ENV GOLANG_VERSION 1.11
 ENV GOLANG_DOWNLOAD_URL https://golang.org/dl/go$GOLANG_VERSION.linux-amd64.tar.gz
-ENV GOLANG_DOWNLOAD_SHA256 674c1091f4712c1cfdcd77ecddafe6aef81cbda740af64a6e3f893ddf3dfb11c
+ENV GOLANG_DOWNLOAD_SHA256 b3fcf280ff86558e0559e185b601c9eade0fd24c900b4c63cd14d1d38613e499
 
 RUN curl -fsSL "$GOLANG_DOWNLOAD_URL" -o golang.tar.gz \
     && echo "$GOLANG_DOWNLOAD_SHA256  golang.tar.gz" | sha256sum -c - \