Consolidate condition on path sources

It matches the comment above more naturally and it's consistent with how
the same thing is checked in other places.

Author: deivid-rodriguez

bundler/lib/bundler/definition.rb

@@ -1056,7 +1056,7 @@ def converge_specs(specs)
         next if @sources_to_unlock.include?(source.name)
 
         # Path sources have special logic
-        if source.instance_of?(Source::Path) || source.instance_of?(Source::Gemspec) || source.instance_of?(Source::Git)
+        if source.is_a?(Source::Path)
           new_spec = source.specs[s].first
           if new_spec
             s.runtime_dependencies.replace(new_spec.runtime_dependencies)