fix(formlyConfig): Removes explicitAsync from formlyConfig.
fix(formlyConfig): Removes explicitAsync from formlyConfig.

This property is no longer being used. It was deprecated in
SHA:4f9d24752abfab9f5064018b3af3ec61e6bd22c2

closes #516

benoror/angular-formly,formly-js/angular-formly,BarryThePenguin/angular-formly,kentcdodds/angular-formly,kwypchlo/angular-formly,ValentinH/angular-formly,ckniffen/angular-formly,kamilkisiela/angular-formly,cynicaldevil/angular-formly,sparty02/angular-formly