Add esm and lib folders to ignore list

[iaarnio]

Reason

Folder esm and lib are left to project folder after running e.g. npm run build.
These folders do not belong to git repository so ignoring them.

Change

Add esm and lib to ignored folders for git.

[codecov]

Codecov Report

Merging #55 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master    #55   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           4      4           
  Lines          56     56           
  Branches       10     10           
=====================================
  Hits           56     56

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[kuitos]

thanks!