Bump build number to 3

[mwcraig]

Checklist

• [x] Used a fork of the feedstock to propose changes
• [x] Bumped the build number (if the version is unchanged)

This PR is necessary only to rebuild; the last merged PR incorrectly used the wrong build number.

ping @jakirkham -- I'm bumping the build number, will merge later this evening...

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[mwcraig]

Merging to cut off the purposeless CI jobs...

[jakirkham]

Thanks @mwcraig :)

[grlee77]

Thanks. It is good to have VTK working with Mayavi again!