handle :version keys in ASD files

[dunn]

ADSF allows :depends_on to be passed a list instead of a string, like (:version "alexandria" "1.0.1"): https://common-lisp.net/project/asdf/asdf.html#The-defsystem-grammar

Currently we aren't parsing that correctly:

$ bin/qi -i cl-graph

---> Installing "cl-graph"
---> Upgrading Qi manifest
   ✓ Qi manifest is already up to date.

-> Preparing to install manifest dependency: "cl-graph"
---> Fetching from "https://github.com/gwkkwg/cl-graph.git"
.... Cloning to WARNING: The CL-Graph system would enjoy having asdf-system-connections
around. See
http://www.cliki.net/asdf-system-connections for details and download
instructions.
"/Users/alex/clones/qi/share/qi/packages/cl-graph-latest/"
.... Checking manifest for transitive dependency: (VERSION metatilities-base
While evaluating the form starting at line 59, column 0
  of #P"/Users/alex/clones/qi/bin/../src/cli.lisp":
Unhandled TYPE-ERROR in thread #<SB-THREAD:THREAD "main thread" RUNNING
                                  {1001F0F173}>:
  The value
    (:VERSION "metatilities-base" "0.6.0")
  is not of type
    (OR (VECTOR CHARACTER) (VECTOR NIL) BASE-STRING SYMBOL CHARACTER)
  when binding SB-IMPL::STRING1