Convert specs to RSpec 3.1.7 syntax with Transpec

# Overview

This pull request is to update the test specifications to be compliant with version 3.x of Rspec. The development/test dependency on Rspec has also been set to ~> 3.1. I also removed a deprecated configuration setting that will always set to `true` for Rspec 3.x. This configuration change was to remove `  config.treat_symbols_as_metadata_keys_with_true_values = true`.

# Transpec Report

This conversion is done by Transpec 2.3.8 with the following command:
    transpec

* 22 conversions
    from: obj.should
      to: expect(obj).to

* 19 conversions
    from: == expected
      to: eq(expected)

* 11 conversions
    from: obj.should_receive(:message)
      to: expect(obj).to receive(:message)

* 9 conversions
    from: obj.stub(:message)
      to: allow(obj).to receive(:message)

* 2 conversions
    from: =~ /pattern/
      to: match(/pattern/)

* 2 conversions
    from: obj.should_not_receive(:message)
      to: expect(obj).not_to receive(:message)

For more details: https://github.com/yujinakayama/transpec#supported-conversions