Bugfix: version absent on install for Forge mods

Prior to this fix, the .r10k-deploy.json file wouldn't have a module
version in it on first install. It would be present after an upgrade or
other modification of an already-present module, just not the first time
the module was added to an environment.

After this commit, the .r10k-deploy.json file is correctly populated
with new-install Forge modules' version numbers.

lib/r10k/module/forge.rb

@@ -75,7 +75,11 @@ def expected_version
 
   # @return [String] The version of the currently installed module
   def current_version
-    @metadata ? @metadata.version : nil
+    if insync?
+      (@metadata ||= @metadata_file.read).nil? ? nil : @metadata.version
+    else
+      nil
+    end
   end
 
   alias version current_version