Update the Oracle section of the administrative guide

The existing docs referenced an older version of the JDBC driver. This
commit just bumps the version of the driver to reflect the most recent
Oracle JDBC release, which is known to work well with Metabase.

docs/administration-guide/databases/oracle.md

@@ -5,12 +5,12 @@ include it as part of Metabase. Luckily, downloading it yourself and making it a
 
 ### Downloading the Oracle JDBC Driver JAR
 
-You can download the JDBC driver from [Oracle's JDBC driver downloads page](http://www.oracle.com/technetwork/database/features/jdbc/default-2280470.html).
-Head to this page, accept the license agreement, and download `ojdbc7.jar`:
+You can download the JDBC driver from [Oracle's JDBC driver downloads page](https://www.oracle.com/technetwork/database/features/jdbc/jdbc-ucp-122-3110062.html).
+Head to this page, accept the license agreement, and download `ojdbc8.jar`:
 
 ![Oracle JDBC Download](../images/oracle_jdbc_download.png)
 
-Before downloading this JAR you may need to sign up for a free account with Oracle.
+Before downloading this JAR you may need to sign up for a free account with Oracle. We recommend downloading version 12.2.0.1 or greater of the Oracle JDBC driver.
 
 
 ### Adding the Oracle JDBC Driver JAR to the Metabase Plugins Directory
@@ -25,14 +25,14 @@ For example, if you're running Metabase from a directory called `/app/`, you sho
 ```bash
 # example directory structure for running Metabase with Oracle support
 /app/metabase.jar
-/app/plugins/ojdbc7.jar
+/app/plugins/ojdbc8.jar
 ```
 
 If you're running Metabase from the Mac App, the plugins directory defaults to `~/Library/Application Support/Metabase/Plugins/`:
 
 ```bash
 # example directory structure for running Metabase Mac App with Oracle support
-/Users/camsaul/Library/Application Support/Metabase/Plugins/ojdbc7.jar
+/Users/camsaul/Library/Application Support/Metabase/Plugins/ojdbc8.jar
 ```
 
 Finally, you can choose a custom plugins directory if the default doesn't suit your needs by setting the environment variable `MB_PLUGINS_DIR`.