Update the date on the license

Also add a note to the release instructions to update the license
file on each release.

.gitlab/issue_templates/NewRelease.md

@@ -39,6 +39,7 @@ git commit -m 'Add release notes for @VERSION@@RC@'
 ```
 -->
 
+  - [ ] Update the version and date in the LICENSE.md file.
   - [ ] Create update version commit:
 
 ```

LICENSE.txt

-VTKm License Version 1.4
+VTKm License Version 1.6
 ========================================================================
 
-Copyright (c) 2014-2019
+Copyright (c) 2014-2021
 Kitware Inc.,
 National Technology & Engineering Solutions of Sandia, LLC (NTESS),
 UT-Battelle, LLC.,