Describe the bug
When I specify a bucket size of 1 with the autograding histogram for a gradeable that has scores from 0 to n it makes a histogram with n buckets and the assignments with scores for n-1 and n grouped into the same bucket.

default plot:

with bucket size=1:

I checked, there are 16 students with the score = 20 and 1 student with the score of 19.

Expected behavior
We should make n+1 buckets in this case.