Ignore `.bundle` when generating test coverage

Fix the code coverage reporting when using `.bundle` to store my gems in
by having SimpleCov ignore that directory. Use of `.bundle` to store my
gems consolidates things since since that directory also holds the
bundler config file. It also keeps a `vendor` directory out of the
project tree for non-Rails projects.  Simplecov was not ignoring that
directory though, which meant that the code coverage numbers I were
seeing locally were wrong (and very frightening). With this change, all
is right with the world once again. 😃

test/helper.rb

@@ -7,6 +7,7 @@ unless ENV['TRAVIS']
   SimpleCov.start('gem') do
     add_filter "/vendor/bundle"
     add_filter "/vendor/gem"
+    add_filter ".bundle"
   end
 end