Fix breaking api change

[FabianMeul]

Because of the change made in this commit (54b9df7#diff-f41e9d04a45c83f3b6f6e630f10117fe) going from an anonymous export to a named export, the library does not work as described in the README.

This PR aims to restore the default behaviour.

Current behaviour of the published package:

const jestModuleNameMapper = require('jest-module-name-mapper').bootstrap();

Expected behaviour in this PR:

const jestModuleNameMapper = require('jest-module-name-mapper')();

[codecov]

Codecov Report

Merging #7 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master        #7   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines            5         5           
  Branches         1         1           
=========================================
  Hits             5         5           

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[FabianMeul]

Thanks for approving the changes!

Any idea on when this might get merged (and published)? :-)

[sebastianmusial]

@FabianMeul Today 🎉