Bump rspec-rails, rake, formtastic and devise

[dependabot-preview[bot]]

Bumps rspec-rails, rake, formtastic and devise. These dependencies needed to be updated together.

Update rspec-rails from 2.14.2 to 3.7.2

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Update rake from 11.3.0 to 12.3.0

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Update formtastic from 2.1.1 to 3.1.5

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Update devise from 3.0.3 to 3.5.10

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