correct the article (a->an) used before ubuntu (uu-boon-tuu) (#9769)
correct the article (a->an) used before ubuntu (uu-boon-tuu) (#9769)

* correct the article used before ubuntu (uu-boon-tuu)

* note for adding additional options in compiling CUDA kernel

tensorflow/docs-l10n,tensorflow/docs,tensorflow/docs,tensorflow/docs