Tutorial: fix WORKSPACE env var export
Tutorial: fix WORKSPACE env var export

As mentioned in mailing list: https://groups.google.com/forum/#!msg/bazel-discuss/Lmmny9foXW0/_tf2ti8KCAAJ

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Change-Id: I8ec654b3cb8a5df28113d1136c511334c1ea99e9
Reviewed-on: https://bazel-review.googlesource.com/#/c/2340/
MOS_MIGRATED_REVID=107923683

davidzchen/bazel-website,bazelbuild/bazel-website,davidzchen/bazel-website,davidzchen/bazel-website,bazelbuild/bazel-website,bazelbuild/bazel-website,davidzchen/bazel-website