update ruby bindings version to 0.1.5, bump deps

[thedavemarshall]

@anakrish this updates the version of the ruby bindings to 0.1.5, and adds a step in bindings/ruby/README#Development for how to generate and update the bindings/ruby/Gemfile.lock file.

[anakrish]

@thedavemarshall Thanks for doing this. Can you also add the following to the ruby api with appropriate names? Policy coverage

• set_enable_coverage
• get_coverage_report
• get_coverage_report_as_colored_string()
• clear_coverage_data

Print statements

• set_gather_prints
• take_prints

That will help me with #250

[thedavemarshall]

@anakrish sure thing, I can take a look at that a little later today!