Changes the default charset for MySQL (#282)

This bug is actually quite sneaky and was breaking exports

CTFd/__init__.py

@@ -43,6 +43,10 @@ def create_app(config='CTFd.config.Config'):
 
         # Creates database if the database database does not exist
         if not database_exists(url):
+            if url.drivername.startswith('mysql'):
+                url.query['charset'] = 'utf8mb4'
+                create_database(url, encoding='utf8mb4')
+            else:
                 create_database(url)
 
         # Register database