Fixing bug with long ints

[jolyonb]

Previously, long integers passed in sample_from or user_constants would cause an error. This fixes that error.

Code:

from mitxgraders import *

grader = MatrixGrader(
    answers='x',
    user_constants={'x': 10 ** 19}
)

grader(None, 'x')

[codecov-io]

Codecov Report

Merging #308 (fbaac50) into master (6cd9cef) will decrease coverage by 0.37%. The diff coverage is 100.00%.

@@             Coverage Diff             @@
##            master     #308      +/-   ##
===========================================
- Coverage   100.00%   99.62%   -0.38%     
===========================================
  Files           32       32              
  Lines         2900     2903       +3     
===========================================
- Hits          2900     2892       -8     
- Misses           0       11      +11     

[jolyonb]

@ChristopherChudzicki You might find this one amusing.