BUG: PyMysql : module 'sqlalchemy' has no attribute 'engine'
- [x] I have checked that this issue has not already been reported.

- [ ] I have confirmed this bug exists on the latest version of pandas.

- [ ] (optional) I have confirmed this bug exists on the master branch of pandas.

---

**Note**: Please read [this guide](https://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports) detailing how to provide the necessary information for us to reproduce your bug.

#### Code Sample, a copy-pastable example

```python
# Your code here
self.conn = pymysql.connect(**info_dic)
pd.read_sql(sql, self.conn)
```

#### Problem description
line 53, in read_data_frame return pd.read_sql(sql, self.conn) File "/usr/local/lib/python3.6/site-packages/pandas/io/sql.py", line 394, in read_sql pandas_sql = pandasSQL_builder(con) File "/usr/local/lib/python3.6/site-packages/pandas/io/sql.py", line 532, in pandasSQL_builder if _is_sqlalchemy_connectable(con): File "/usr/local/lib/python3.6/site-packages/pandas/io/sql.py", line 86, in _is_sqlalchemy_connectable return isinstance(con, sqlalchemy.engine.Connectable) AttributeError: module 'sqlalchemy' has no attribute 'engine'

[this should explain **why** the current behaviour is a problem and why the expected output is a better solution]

#### Expected Output

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

<details>

[paste the output of ``pd.show_versions()`` here leaving a blank line after the details tag]
INSTALLED VERSIONS
------------------
commit: None
python: 3.6.1.final.0
python-bits: 64
OS: Linux
OS-release: 4.4.224-1.el7.elrepo.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.utf8
LOCALE: en_US.UTF-8

pandas: 0.20.3
pytest: None
pip: 10.0.1
setuptools: 28.8.0
Cython: 0.28.1
numpy: 1.14.0
scipy: 1.0.0
xarray: None
IPython: None
sphinx: None
patsy: 0.5.0
dateutil: 2.6.1
pytz: 2017.3
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 2.2.2
openpyxl: 2.5.2
xlrd: 1.1.0
xlwt: None
xlsxwriter: None
lxml: 4.5.2
bs4: None
html5lib: None
sqlalchemy: 1.2.4
pymysql: 0.8.0
psycopg2: None
jinja2: None
s3fs: None
pandas_gbq: None
pandas_datareader: None


</details>
