Update and fix CI status badges

[anvega]

This PR updates and fixes the CI status badges in the README.

Changes made:

1. Removed redundant text labels preceding the badges.
2. Corrected the broken Travis CI badge and URL and switched to shields.io for the badge to include the logo.
3. Updated the CircleCI badge to use the shield style for visual consistency with the other badge.

Note: This is a purely cosmetic change to the markdown file. It does not add new features, affect input/output behavior, or alter the list of algorithms. No version bump or downstream project updates are required.

[baentsch]

Thanks for fixing #1827, @anvega !

@dstebila @SWilson4 Now that more contributions come in, may I suggest we somehow begin to track/actively "manage" open issues (to not rely on me to remember them?) Something like a "best (solved :) by" date for each, maybe (after which they get checked again and maybe re/prioritized or dropped?)

[dstebila]

@dstebila @SWilson4 Now that more contributions come in, may I suggest we somehow begin to track/actively "manage" open issues (to not rely on me to remember them?) Something like a "best (solved :) by" date for each, maybe (after which they get checked again and maybe re/prioritized or dropped?)

Yes, we've definitely fallen behind on issue triage and prioritization. I don't think it's possible to set that type of metadata for an issue directly, unless we use tags. Maybe project boards would be good for this? @planetf1, any recommendations from your experience playing around with Github project boards?