Enhancement: Run 'composer normalize'

[localheinz]

This PR

• requires localheinz/composer-normalize
• runs composer normalize in vendor target and on Travis CI
• updates composer itself to latest snapshot (see composer 1.7 doesn't work with wp-cli/wp-cli package composer/composer#7516 (comment))

[codecov]

Codecov Report

Merging #94 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             master    #94   +/-   ##
=======================================
  Coverage       100%   100%           
  Complexity       64     64           
=======================================
  Files             4      4           
  Lines           170    170           
=======================================
  Hits            170    170

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