FIX(composer.json): remove cakephp/datasource

remove cakephp/datasource, because it's now include in cakephp/cakephp 3.4.0

Refs: #751
2 jobs for 751_composer.json_remove.cakephp.datasource in 1 minute and 47 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #26644
phpcs

00:00:27

passed #26645
phpunit

00:01:46

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