Update to Laravel 6 & 7, + PHP 7.4 compatible

[lauhakari]

This might be nice to have.

What I could notice no big changes and tests passed.

[ben182]

Addressing #94

[mnvx]

Travis fails on PHP 5.6. Maybe will be better to just remove 5.6 from Travis config, because Laravel 6 supports PHP 7.2+

[weidmaster]

Merging this does fix the issue, as it is only a parenthesis error in the ternary condition. Please accept it so we can update in our composer json. Thank you.

[vincentkedison]

Please help to release it to packagist. I use ben182/laravel-auto-translate, and this package depends on themsaid/laravel-langman. Causing error on php 7.4

ErrorException  : Unparenthesized `a ? b : c ? d : e` is deprecated. Use either `(a ? b : c) ? d : e` or `a ? b : (c ? d : e)`

Thank you