Zhuoyang change commission to double

[zhuoyang125]

increase the range of commission to avoid overflow errors

[codecov-commenter]

Codecov Report

Merging #184 (f6caa4c) into master (dfbc77d) will increase coverage by 0.14%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master     #184      +/-   ##
============================================
+ Coverage     54.84%   54.98%   +0.14%     
  Complexity      556      556              
============================================
  Files           107      107              
  Lines          2281     2275       -6     
  Branches        282      281       -1     
============================================
  Hits           1251     1251              
+ Misses          933      927       -6     
  Partials         97       97              

Impacted Files	Coverage Δ
...in/java/seedu/siasa/commons/util/CurrencyUtil.java	0.00% <0.00%> (ø)
...va/seedu/siasa/logic/commands/DownloadCommand.java	2.32% <0.00%> (+0.19%)	⬆️
src/main/java/seedu/siasa/model/Model.java	100.00% <ø> (ø)
src/main/java/seedu/siasa/model/ModelManager.java	74.69% <ø> (ø)
src/main/java/seedu/siasa/model/Siasa.java	42.85% <0.00%> (ø)
...ava/seedu/siasa/model/policy/UniquePolicyList.java	78.43% <0.00%> (+4.35%)	⬆️
src/main/java/seedu/siasa/ui/GuideWindow.java	0.00% <ø> (ø)

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[sherrpass]

LGTM!

[sherrpass]

Isn't download supposed to create a csv file? Maybe we can look into creating a separate issue and pr for this.