Fix typo

templates/env.sample.j2

@@ -2,7 +2,7 @@
 export SQL_HOST=127.0.0.1
 export SQL_PORT=3306
 export SQL_DATABASE="{{ don_sql_database }}"
-export SQL_USER="{{ don_sql_user }}"
+export SQL_USER={{ don_sql_user }}
 export SQL_PASSWORD="{{ don_sql_password }}"
 
 # Phinx configuration