fix typo in example in aspects docs
fix typo in example in aspects docs

The attribute for the source list is "srcs", not "src".

Closes #2098.

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Reviewed-on: https://github.com/bazelbuild/bazel/pull/2098
MOS_MIGRATED_REVID=139380743

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