show_versions fails on master with latest lxml
#### Code Sample, a copy-pastable example if possible

```python
[ins] In [1]: import pandas as pd
p
[ins] In [2]: pd.show_versions()
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-2-3d232a07e144> in <module>
----> 1 pd.show_versions()

~/workspace/pandas/pandas/util/_print_versions.py in show_versions(as_json)
    107             else:
    108                 mod = importlib.import_module(modname)
--> 109             ver = ver_f(mod)
    110             deps_blob.append((modname, ver))
    111         except ImportError:

~/workspace/pandas/pandas/util/_print_versions.py in <lambda>(mod)
     86         ("xlwt", lambda mod: mod.__VERSION__),
     87         ("xlsxwriter", lambda mod: mod.__version__),
---> 88         ("lxml", lambda mod: mod.etree.__version__),
     89         ("bs4", lambda mod: mod.__version__),
     90         ("html5lib", lambda mod: mod.__version__),

AttributeError: module 'lxml' has no attribute 'etree'
```

#### Expected Output

This seems to work OK on 0.23.4 (output below).

Let me know if there are other potential factors you'd like me to check

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

<details>

[ins] In [5]: pd.show_versions()

INSTALLED VERSIONS
------------------
commit: None
python: 3.7.1.final.0
python-bits: 64
OS: Darwin
OS-release: 18.0.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.23.4
pytest: 3.9.2
pip: 18.1
setuptools: 40.6.2
Cython: 0.28.5
numpy: 1.15.2
scipy: None
pyarrow: None
xarray: 0.10.9
IPython: 7.1.1
sphinx: None
patsy: 0.5.0
dateutil: 2.7.5
pytz: 2018.5
blosc: None
bottleneck: 1.2.1
tables: None
numexpr: 2.6.8
feather: None
matplotlib: 3.0.0
openpyxl: None
xlrd: 1.1.0
xlwt: 1.3.0
xlsxwriter: None
lxml: 4.2.5
bs4: 4.6.0
html5lib: 1.0.1
sqlalchemy: 1.2.12
pymysql: None
psycopg2: None
jinja2: 2.8.1
s3fs: None
fastparquet: None
pandas_gbq: 0.6.1+2.gd98c621
pandas_datareader: 0.7.0
</details>
