doc: fix versions.json

Get rid of trailing comma and pre-1.0.0 versions.

Signed-off-by: Bartosz Gentkowski <bartosz.gentkowski@nordicsemi.no>

Author: b-gent

doc/versions.json

@@ -1,7 +1,5 @@
 [
     "2.0.99",
     "2.0.0",
-    "1.0.0",
-    "0.9.0",
-    "0.8.0",
+    "1.0.0"
 ]