How to add non-Stackage GitHub dependency

[asrvsn]

It's unclear to me from the docs how to do so. I've added the following to my stack.yaml:

packages:
- location: .
- location: 
    git: [email protected]:atzeus/HMap
    commit: c6fbde4aaeb7dff42f157f6fdd3f95375852f065
    extra-dep: true

Yet stack install still yields

--  Failure when adding dependencies:    
     hmap: needed (-any), stack configuration has no specified version
     needed for package alphasheets-0.1.0.0

[mgsloan]

Package names are case sensitive. You want HMap in build-deps.

It would be great to have typo suggestions in more places - #1748