DOCS-391 1.8 release notes link on installation page

Author: Sam Kleinman

source/installation.txt

@@ -36,6 +36,6 @@ while v2.1 and v2.3 is a development version.
 - Previous Stable Releases
 
   - :doc:`/release-notes/2.0`
-  - :wiki:`v1.8 Release Notes <1.8+Release+Notes>`
+  - :doc:`/release-notes/1.8`
 
 - Current Development Release (v2.3-series)