making sure library up to date
Merge branch 'master' of git://github.com/openwebwork/webwork-open-problem-library
Fix bug 3030
Merge branch 'master' of github.com:openwebwork/webwork-open-problem-library
Fix bug 3031
Fixed bug 3032
Merge pull request #63 from Dick-Lane/master

Replace  black  with  'black'  to avoid a warning message:
Small fix.
Fix answer listed as the correct answer

The answer listed as the correct answer was incorrect due to an oversight (the correct answer was commented out).  Also fixed the custom answer checker by removing double quotes (minor improvement).
Remove empty hint
Merge branch 'master' of github.com:openwebwork/webwork-open-problem-library
Fix bug 3034
Fix bug 3035
Fix bug 3037
Small fix.
Merge branch 'master' of git://github.com/openwebwork/webwork-open-problem-library
Improve vector formatting.
Improve formatting.
Correct wording for options.
Correct image file name.