[Misc] Fix a bug in util.py

[Rullec]

Hi all,
When I am testing ti.info, I found that there is a literally typo in our util.py.
It will crash all logging APIs. :(

[k-ye]

Thx!

[Rullec]

Thx!

With pleasure :)

[codecov]

Codecov Report

Merging #1327 into master will increase coverage by 0.12%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1327      +/-   ##
==========================================
+ Coverage   85.35%   85.48%   +0.12%     
==========================================
  Files          19       19              
  Lines        3374     3375       +1     
  Branches      630      630              
==========================================
+ Hits         2880     2885       +5     
+ Misses        362      358       -4     
  Partials      132      132              

Impacted Files	Coverage Δ
python/taichi/lang/expr.py	89.82% <100.00%> (+0.06%)	⬆️
python/taichi/lang/util.py	64.07% <0.00%> (+2.39%)	⬆️

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