Travis failing to publish code coverage to Coveralls

[j-richey]

Describe the bug
Travis has stopped sending code coverage reports to Coveralls. This was noticed when creating the v0.1.2 release.

First, the job that pushes the code coverage report was not appearing in the build matrix. After a bit of hacking to get it to appear in the matrix and get the job to run there was a problem with the cargo coveralls command:

error: failed to parse lock file at: /home/travis/build/j-richey/open_ttt_lib/Cargo.lock

Steps to reproduce

1. Create a branch to kick off a Travis build.
2. Observe Travis' build matrix does not include an stable Linux Rust job.
3. Remove the jobs/exclude keys and push the change.
4. Observe that two stable Linux Rust jobs in the matrix.
5. However, the one that tries to push to coveralls ends with the error message "error: failed to parse lock file at: /home/travis/build/j-richey/open_ttt_lib/Cargo.lock"

Library Version:
Use the .travis.yaml from 0.1.2 build was used.

Expected behavior
Code coverage should be generated with every Travis build.

Additional context
Here is a resource that might be useful when debugging .travis.yaml file issues: https://config.travis-ci.com/explore

[j-richey]

After some research I found the following:

• Currently, the build is using the cargo-travis along with kcov to generate coverage data and submit it to coveralls. There is a known issue parsing the Cargo.lock file.
• The cargo-tarpaulin crate might be more useful to us. It is more widely used than cargo-travis, seems to get more frequent updates, supports generating local coverage reports, and contains support for pushing to coveralls.

[j-richey]

The project has been updated to use cargo-tarpaulin and its successfully publishing to Coveralls. Additionally, the CONTRIBUTING.md file has been updated on how to run cargo-tarpaulin locally.