GH-571: [Docs] Fix redirect pattern (#575)

Fixes #571.

We need to use `^/java/$` not `^/$` because we deploy our website to
`https://.../java/` not `https://.../`.

Author: kou

.htaccess

@@ -15,4 +15,4 @@
 # specific language governing permissions and limitations
 # under the License.
 
-RedirectMatch permanent "^/$" /current/
+RedirectMatch permanent "^/java/$" /java/current/