flask_sqlalchemy example : different types with the same name in the schema: EmployeeConnection, EmployeeConnection.

Hi,

I followed the instruction to use the flask_sqlalchemy example with a Python 2.7 version, when I run the app.py script, I've got the following error :

```
(py27) λ python app.py
Traceback (most recent call last):
File "app.py", line 7, in
from schema import schema
File "D:\Thomas\Dev\graphene-sqlalchemy\examples\flask_sqlalchemy\schema.py", line 60, in
schema = graphene.Schema(query=Query, types=[Department, Employee, Role])

....

File "D:\Programmes\Anaconda2\envs\py27\lib\site-packages\graphene\types\typemap.py", line 99, in graphene_reducer
).format(_type.graphene_type, type)
AssertionError: Found different types with the same name in the schema: EmployeeConnection, EmployeeConnection.
```

What am I doing wrong ?

Thank you

Reproduce the failure by running examples/flask_sqlalchemy/app.py with the Python 2.7 setup described, then inspect schema.py around line 60 where the Graphene schema is created. Trace why EmployeeConnection is registered twice and confirm the example starts without the assertion.

由索引模型根據 Issue 內容生成。