pd.to_hdf throws AttributeError: module 'tables' has no attribute '__version__'
#### Code Sample, a copy-pastable example if possible

```python
import pandas as pd                                                     
                                                                         
df = pd.DataFrame({'A': [1, 2, 3], 'B': [4, 5, 6]},index=['a', 'b', 'c'])
df.to_hdf('data.h5', key='df', mode='w')               
```
#### Problem description

[The standard example (see above) throws the following error:
```python
Traceback (most recent call last):
  File "test.py", line 5, in <module>
    df.to_hdf('data.h5', key='df', mode='w')
  File "/zpool/software/apps/anaconda3/lib/python3.7/site-packages/pandas/core/generic.py", line 1996, in to_hdf
    return pytables.to_hdf(path_or_buf, key, self, **kwargs)
  File "/zpool/software/apps/anaconda3/lib/python3.7/site-packages/pandas/io/pytables.py", line 278, in to_hdf
    complib=complib) as store:
  File "/zpool/software/apps/anaconda3/lib/python3.7/site-packages/pandas/io/pytables.py", line 491, in __init__
    self.open(mode=mode, **kwargs)
  File "/zpool/software/apps/anaconda3/lib/python3.7/site-packages/pandas/io/pytables.py", line 576, in open
    tables = _tables()
  File "/zpool/software/apps/anaconda3/lib/python3.7/site-packages/pandas/io/pytables.py", line 249, in _tables
    if LooseVersion(tables.__version__) < LooseVersion('3.0.0'):
AttributeError: module 'tables' has no attribute '__version__'
```
I did a fresh install of anaconda version 4.6.11 and the output of 
```
conda list pytables
```
is
```
pytables                  3.4.4            py37ha205bf6_0
```
=> pytables version should be bigger than 3.0.0
]

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#### Expected Output

#### Output of ``pd.show_versions()``

<details>

[INSTALLED VERSIONS
------------------
commit: None
python: 3.7.3.final.0
python-bits: 64
OS: Linux
OS-release: 4.15.0-47-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.23.4
pytest: 4.3.1
pip: 19.0.3
setuptools: 40.8.0
Cython: 0.29.6
numpy: 1.15.1
scipy: 1.1.0
pyarrow: None
xarray: None
IPython: 7.4.0
sphinx: 1.8.5
patsy: 0.5.0
dateutil: 2.8.0
pytz: 2018.9
blosc: None
bottleneck: 1.2.1
tables: None
numexpr: 2.6.8
feather: None
matplotlib: 2.2.3
openpyxl: 2.6.1
xlrd: 1.2.0
xlwt: 1.3.0
xlsxwriter: 1.1.5
lxml: 4.3.2
bs4: 4.7.1
html5lib: 1.0.1
sqlalchemy: 1.3.1
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None
]

</details>
