Merge pull request #7554 from rubygems/full-gem-path-should-be-string

Fix crash with development bundler binstub

(cherry picked from commit 0c68576)

Author: deivid-rodriguez

bundler/spec/support/activate.rb

@@ -5,5 +5,5 @@
 
 require_relative "path"
 bundler_gemspec = Spec::Path.loaded_gemspec
-bundler_gemspec.instance_variable_set(:@full_gem_path, Spec::Path.source_root)
+bundler_gemspec.instance_variable_set(:@full_gem_path, Spec::Path.source_root.to_s)
 bundler_gemspec.activate if bundler_gemspec.respond_to?(:activate)