Include CodeCov in Travis configuration

[mkainula]

Fixes #383

Checklist

• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the [Contribution Guide] and my PR follows them.
• I updated my branch with the master branch.
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation about the functionality in the appropriate .md file
• I have added in line documentation to the code I modified

Short description of what this PR does:

• Adds Codecov to travis.yml
• Adds JaCoCo plugin to pom.xml

If you have questions, please send an email to Sendgrid, or file a Github Issue in this repository.

[SendGridDX]

All committers have signed the CLA.

[thinkingserious]

@mkainula

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[mbernier]

@mkainula it looks like the jacoco plugin is causing this to fail. I was thinking that we're using another plugin to run tests - would it be possible to see if that plugin can pass the unitest data to codecov?

@andy-trimble for sanity check, bc this is Java so I am probably incorrect here.

[andy-trimble]

Yeah. That's a weird instrumentation error. It's unclear why it's failing though. It might be a JaCoCo version issue. It might be worth trying it with a different, pinned version.

[mbernier]

@mkainula can you please try a different jacoco plugin version?

[childish-sambino]

Closing due to inactivity.