Shrink of commands stops at first level (regression 1.8.0)

[dubzzz]

More at https://travis-ci.org/dubzzz/fast-check/jobs/466197284

[dubzzz]

 1) CommandsArbitrary (seed: 1544476043199) commands Should print only the commands corresponding to the failure: AssertionError [ERR_ASSERTION]: Expected the only played command to be 'failure', got: success,failure for steps 0,1 + expected - actual -success,failure +failure at Context.<anonymous> (test/e2e/model/CommandsArbitrary.spec.ts:60:14) 

[dubzzz]

Bug might be the line 53 of https://github.com/dubzzz/fast-check/blob/master/src/check/model/commands/CommandsArbitrary.ts

size has to be used with shrunkOnce = false

A test have to be designed to detect more easily such issues in the future :)

[dubzzz]

It seems to be a regression coming from #235 in 1.8.0. I am currently working on patch that should be integrated into 1.8.2 release (fixes the shrink of fc.commands).