This should fix the following case which uses "HTBResources.bundle" as resource.
```
% rake
ERROR! An iOS application cannot be installed if it contains a directory called `resources'. Please rename the directory at path `vendor/Pods/Resources/HTBResources.bundle' to, for instance, `vendor/Pods/Resources/assets'.
````
it cause an error If app.resources_dirs has nested array
app.resources_dirs << ['Images']
```
% rake
rake aborted!
no implicit conversion of Array into String
/Library/RubyMotion/lib/motion/project/template/ios.rb:51:in `exists?'
/Library/RubyMotion/lib/motion/project/template/ios.rb:51:in `block in pre_build_actions'
/Library/RubyMotion/lib/motion/project/template/ios.rb:50:in `each'
/Library/RubyMotion/lib/motion/project/template/ios.rb:50:in `pre_build_actions'
/Library/RubyMotion/lib/motion/project/template/ios.rb:67:in `block (2 levels) in <top (required)>'
/Library/RubyMotion/lib/motion/project/template/ios.rb:122:in `block in <top (required)>'
Tasks: TOP => build:simulator
(See full trace by running task with --trace)
```
This bug is introduced by 064672443d
% motion create hello && cd hello
% rm -rf resources
% rake
rake aborted!
No such file or directory @ dir_initialize - ./resources
/Library/RubyMotion/lib/motion/project/template/ios.rb:51:in `open'
/Library/RubyMotion/lib/motion/project/template/ios.rb:51:in `entries'
/Library/RubyMotion/lib/motion/project/template/ios.rb:51:in `block in pre_build_actions'
/Library/RubyMotion/lib/motion/project/template/ios.rb:50:in `each'
/Library/RubyMotion/lib/motion/project/template/ios.rb:50:in `pre_build_actions'
/Library/RubyMotion/lib/motion/project/template/ios.rb:66:in `block (2 levels) in <top (required)>'
/Library/RubyMotion/lib/motion/project/template/ios.rb:121:in `block in <top (required)>'
Tasks: TOP => build:simulator
(See full trace by running task with --trace)
Since spec.add_development_dependency "rake" is already in the gemspec template, we don't need it in the Gemfile and we should always defer to the gemspec for our dependencies except for advanced use cases.
