Avoid nesting cloned OGM repos inside themselves

Providing both `directory` and `path` to Git.clone results in
the repo being cloned into a directory nested inside itself.

This may be a fix for #144.

lib/geo_combine/harvester.rb

@@ -73,7 +73,7 @@ def clone(repo = nil)
       return 0 if File.directory? repo_path
 
       repo_url = "https://github.com/OpenGeoMetadata/#{repo}.git"
-      Git.clone(repo_url, repo, path: repo_path, depth: 1) && 1
+      Git.clone(repo_url, nil, path: ogm_path, depth: 1) && 1
     end
 
     private

spec/lib/geo_combine/harvester_spec.rb

@@ -75,9 +75,9 @@
       harvester.clone(repo_name)
       expect(Git).to have_received(:clone).with(
         repo_url,
-        repo_name, {
+        nil, {
           depth: 1, # shallow clone
-          path: repo_path
+          path: harvester.ogm_path
         }
       )
     end