inserted driver for solving issue #348

Using SQL-Alchemy needs the attribute driver.
I simply added `crate-python` as the driver name.

This solves https://github.com/crate/crate-python/issues/348

Author: Barry1

src/crate/client/sqlalchemy/dialect.py

@@ -159,6 +159,7 @@ def process(value):
 
 class CrateDialect(default.DefaultDialect):
     name = 'crate'
+    driver = 'crate-python'
     statement_compiler = CrateCompiler
     ddl_compiler = CrateDDLCompiler
     type_compiler = CrateTypeCompiler