Remove the 'v' from v2.0-preview

Looks like _index shouldn't have a leading v. Something else prefixes a
v on the dropdown.

Signed-off-by: Nic Cope <[email protected]>

Author: negz

content/v2.0-preview/_index.md

@@ -2,7 +2,7 @@
 title: "Overview"
 weight: -1
 cascade:
-    version: "v2.0-preview"
+    version: "2.0-preview"
 ---
 
 {{< img src="/media/banner.png" alt="Crossplane Popsicle Truck" size="large" >}}