Bump default MariaDB to 10.4 (#18)

Author: adamchainz

.env

@@ -2,5 +2,5 @@ PYTHON_VERSION=3.6
 POSTGRES_VERSION=9.6
 POSTGIS_VERSION=2.5
 MYSQL_VERSION=8
-MARIADB_VERSION=10.3
+MARIADB_VERSION=10.4
 PIP_CACHE_VOLUME=pip-cache

README.md

@@ -100,7 +100,7 @@ To enter a bash shell within the container, run:
 | `PYTHON_VERSION` | `3.6` | The python version to run tests against |
 | `POSTGRES_VERSION` | `9.6` | The version of Postgres to use |
 | `MYSQL_VERSION` | `8` | The mysql version to use |
-| `MARIADB_VERSION` | `10.3` | The mariadb version to use |
+| `MARIADB_VERSION` | `10.4` | The mariadb version to use |
 
 
 ## Why?