Don't try to delete Gemfile.lock if it doesn't exist already

Author: jonleighton

test/support/sass_rails_test_case.rb

@@ -66,7 +66,7 @@ def within_rails_app(name, without_gems = [], gem_options = $gem_options)
       Dir.chdir(tmpdir) do
         gem_options.each {|name, options| modify_gem_entry name, options}
         without_gems.each {|name| remove_gem name}
-        FileUtils.rm("Gemfile.lock")
+        FileUtils.rm("Gemfile.lock") if File.exist?("Gemfile.lock")
         runcmd "bundle install --verbose"
         yield tmpdir
       end