foreign key constraint incorrectly formed
Solved by replacing db_table with table_name 
db_table is from an older version (2.x.x). Probably it also caused the foreignKeyConstraint Error
When I want to create a table I get the error foreign_key

> ERROR	session[5924]: (1005, 'Can\'t create table `example_database`.`example_table` (errno: 150 "Foreign key constraint is incorrectly formed")')

example_table is specified as:
```python
class Example_Table(BaseModel):
    id = PrimaryKeyField()
    example_table2 = ForeignKeyField(Modul)
    class Meta:
        db_table = 'Example_Table'
```
after i defined BaseModel:
```python
class BaseModel(Model):
    class Meta:
        database = database
```
and database is my MySQLDatabase Object.
The Problem is, why doesnt the foreign key constraint work and why are the tables all saved in Lowercase, but I defined them in Uppercase

If I run the program again, It creates the tables but gives me a duplicate key_name error 

Version: peewee==3.0.17

