HEMCO submod update: Merge PR #276 (Update issue templates)

This commit informs the GCHP superproject about the following
commits that were pushed to the GitHub geoschem/geos-chem repository:

e6d0708 Merge PR #276 (Update Github issue templates to use issue forms)

PR #276 now uses issue template forms to make sure that all users
who open issues provide the required information.

Signed-off-by: Bob Yantosca <[email protected]>