Bundler complaining about duplicate dependency on spreadsheet

[chrhansen]

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Using carrierwave (0.9.0)
The validation message from Rubygems was:
duplicate dependency on spreadsheet (>= 0, development), (>= 0) use:
add_runtime_dependency 'spreadsheet', '>= 0', '>= 0'
Using omniauth-github (1.1.1)
Using to_xls (1.5.3) from git://github.com/splendeo/to_xls.git (at master)
Using exception_notification (4.0.1)
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