fix python lower than 2.7.9 is not support algorithms_guaranteed

[abitduck]

No description provided.

[codecov-io]

Codecov Report

Merging #2 into master will decrease coverage by 1%.
The diff coverage is 50%.

@@            Coverage Diff            @@
##           master      #2      +/-   ##
=========================================
- Coverage   89.61%   88.6%   -1.01%     
=========================================
  Files           2       2              
  Lines          77      79       +2     
=========================================
+ Hits           69      70       +1     
- Misses          8       9       +1

Impacted Files	Coverage Δ
rehash/__init__.py	86.15% <50%> (-1.15%)	⬇️

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