NOJIRA: Update link to individual contributor license agreement

[ChristianMurphy]

Checklist

• the individual contributor license agreement is signed
• commit message follows commit guidelines
• documentation is changed or added

Description of change

ICLA pdf has been removed, the online submission form is now recommended.

[coveralls]

Coverage increased (+0.01%) to 22.89% when pulling 7cc7239 on ChristianMurphy:NOJIRA-icla-link into 554fae3 on Jasig:master.

[apetro]

I'm surprised the PDF was removed. As I understand it that was not intended and I'll follow up on that.

Nonetheless, the not-PDF-specific URL path is superior in every way and it's an improvement to update CONTRIBUTING.md in this way.

[vertein]

I just printed off a copy, and I also looked for the pdf. I just printed off a copy of the web form. It seemed weird, but maybe because I expected the pdf.

[ChristianMurphy]

@vertein You're right, the ICLA page looks off in print mode. It could use a print stylesheet to improve the appearance.

[bjagg]

LGTM! 🥇