Use single ellipsis unicode character by default

[markhicken]

Resolves #6

Let me know what you think! Or just merge it if you like. :)

[codecov]

Codecov Report

Merging #11 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #11   +/-   ##
=======================================
  Coverage   30.76%   30.76%           
=======================================
  Files           1        1           
  Lines          26       26           
  Branches        2        2           
=======================================
  Hits            8        8           
  Misses         17       17           
  Partials        1        1           

Impacted Files	Coverage Δ
src/truncateString.js	30.76% <ø> (ø)

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