fix #3107: code block indentation in docs (H2 to PG)

docs/operations-guide/start.md

@@ -144,15 +144,15 @@ Metabase provides a custom migration command for upgrading H2 application databa
 1. Shutdown your Metabase instance so that it's not running.  This ensures no accidental data gets written to the db while migrating.
 2. Make a backup copy of your H2 application database by following the instructions in [Backing up Metabase Application Data](#backing-up-metabase-application-data).  Safety first!
 3. Run the Metabase data migration command using the appropriate environment variables for the target database you want to migrate to.  You can find details about specifying MySQL and Postgres databases at [Configuring the application database](#configuring-the-metabase-application-database).  Here's an example of migrating to Postgres.
-
-    export MB_DB_TYPE=postgres  
-    export MB_DB_DBNAME=metabase  
-    export MB_DB_PORT=5432  
-    export MB_DB_USER=<username>  
-    export MB_DB_PASS=<password>  
-    export MB_DB_HOST=localhost  
-    java -jar metabase.jar load-from-h2 <path-to-metabase-h2-database-file>
-
+```
+export MB_DB_TYPE=postgres
+export MB_DB_DBNAME=metabase
+export MB_DB_PORT=5432
+export MB_DB_USER=<username>
+export MB_DB_PASS=<password>
+export MB_DB_HOST=localhost
+java -jar metabase.jar load-from-h2 <path-to-metabase-h2-database-file>
+```
 It is expected that you will run the command against a brand new (empty!) database and Metabase will handle all of the work of creating the database schema and migrating the data for you.
 
 **Note:** It is required that wherever you are running this migration command can connect to the target MySQL or Postgres database.  So if you are attempting to move the data to a cloud database make sure you take that into consideration.