Export ALBERT main layer in TensorFlow
closes #3262 
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/3354?src=pr&el=h1) Report
> Merging [#3354](https://codecov.io/gh/huggingface/transformers/pull/3354?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/3bedfd334763cb5676c2fe92705390ac57d8de5f&el=desc) will **increase** coverage by `0.07%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/3354/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/3354?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #3354      +/-   ##
==========================================
+ Coverage   77.61%   77.68%   +0.07%     
==========================================
  Files         100      100              
  Lines       16938    16938              
==========================================
+ Hits        13146    13159      +13     
+ Misses       3792     3779      -13     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/3354?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/\_\_init\_\_.py](https://codecov.io/gh/huggingface/transformers/pull/3354/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9fX2luaXRfXy5weQ==) | `98.92% <ø> (ø)` | |
| [src/transformers/modeling\_tf\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/3354/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl91dGlscy5weQ==) | `88.55% <0.00%> (+2.32%)` | :arrow_up: |

------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/3354?src=pr&el=footer). Last update [3bedfd3...77a2a4c](https://codecov.io/gh/huggingface/transformers/pull/3354?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
