Fix #469

[YasushiMiyata]

Description of the problems or issues

Is your pull request related to a problem? Please describe. 'get_max_row_num' is missing in 'fonduer.utils.data_model_utils.tabular'

Does your pull request fix any issue. Fix #469

Description of the proposed changes

Add get_max_row_num to tabular.py and revise the test code in test_tabular.py.

Test plan

Have revised the test code in test_tabular.py and done unit test.

Checklist

• [x] I have updated the documentation accordingly.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.
• [x] I have updated the CHANGELOG.rst accordingly.

[codecov-commenter]

Codecov Report

Merging #480 into master will increase coverage by 0.05%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #480      +/-   ##
==========================================
+ Coverage   85.77%   85.83%   +0.05%     
==========================================
  Files          88       88              
  Lines        4554     4559       +5     
  Branches      847      848       +1     
==========================================
+ Hits         3906     3913       +7     
+ Misses        465      464       -1     
+ Partials      183      182       -1     

Flag	Coverage Δ
#unittests	85.83% <100.00%> (+0.05%)	:arrow_up:

Impacted Files	Coverage Δ
src/fonduer/utils/data_model_utils/tabular.py	100.00% <100.00%> (ø)
src/fonduer/parser/visual_linker.py	84.18% <0.00%> (+0.93%)	:arrow_up: