fix ProtoList with int type

[nitoqq]

Related to issue #3

[codecov-io]

Codecov Report

Merging #4 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master     #4   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           3      3           
  Lines         112    113    +1     
  Branches       22     23    +1     
=====================================
+ Hits          112    113    +1

Impacted Files	Coverage Δ
mercator/__init__.py	100% <100%> (ø)	⬆️

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