Run Go1.9 and 386 on Travis

[dfawley]

Fixes #1473

[dfawley]

Looks like Travis doesn't support Go1.9 yet:

$ GIMME_OUTPUT=$(gimme 1.9.x | tee -a $HOME/.bashrc) && eval "$GIMME_OUTPUT"
I don't have any idea what to do with '1.9.x'.
  (using type 'auto')
$ export GOPATH=$HOME/gopath
$ export PATH=$HOME/gopath/bin:$PATH
$ mkdir -p $HOME/gopath/src/google.golang.org/grpc
$ rsync -az ${TRAVIS_BUILD_DIR}/ $HOME/gopath/src/google.golang.org/grpc/
$ export TRAVIS_BUILD_DIR=$HOME/gopath/src/google.golang.org/grpc
$ cd $HOME/gopath/src/google.golang.org/grpc
0.02s
$ gimme version
v1.0.0
$ go version
go version go1.7.4 linux/amd64

But, travis-ci/travis-build#1148 just added it...

[menghanl]

Also make this 1.9*?

[HelloGrayson]

@dfawley looks like gimme has 1.9 now:

google.golang.org/grpc-go - [go1.9] » gimme 1.9

unset GOOS;
unset GOARCH;
export GOROOT='/Users/grayson/.gimme/versions/go1.9.darwin.amd64';
export PATH="/Users/grayson/.gimme/versions/go1.9.darwin.amd64/bin:${PATH}";
go version >&2;