Update GFS version to v16.3.13 in index.rst (#2256)

GFSv16.3.13 WAFS update was implemented

Refs #2013

Author: KateFriedman-NOAA

docs/source/index.rst

@@ -10,7 +10,7 @@ Status
 ======
 
 * State of develop (HEAD) branch: GFSv17+ development
-* State of operations (dev/gfs.v16 branch): GFS v16.3.12 `tag: [gfs.v16.3.12] <https://github.com/NOAA-EMC/global-workflow/releases/tag/gfs.v16.3.12>`_
+* State of operations (dev/gfs.v16 branch): GFS v16.3.13 `tag: [gfs.v16.3.13] <https://github.com/NOAA-EMC/global-workflow/releases/tag/gfs.v16.3.13>`_
 
 =============
 Code managers