Update CONTRIBUTING.md to reflect new DB_URL (#140)

Since we recently switched over from using `asyncpg` to `psycopg2` as the DBAPI for SQLAlchemy, we want this to be accurately documented as the default `DB_URL` set as the environment variable

Signed-off-by: Robin <[email protected]>

CONTRIBUTING.md

@@ -141,7 +141,7 @@ You'll need to have the following environment variables set.
 | | | | |
 | `EMAIL_RECIPIENT` | str | "[email protected]" | The recipient address of report emails |
 | `BCC_RECIPIENTS` | set | set() | Additional addresses that should be BCC'd in email reports. Defaults to an empty set. |
-| `DB_URL` | str | "postgresql+asyncpg://postgres:postgres@localhost:5432" | PostgreSQL database connection string |
+| `DB_URL` | str | "postgresql+psycopg2://postgres:postgres@localhost:5432" | PostgreSQL database connection string |
 | | | | |
 | `SENTRY_DSN` | str | "" | Sentry Data Source Name (DSN) |
 | `SENTRY_ENVIRONMENT` | str | "" | Sentry environment |