Add alias in MetaServiceProvider for injection

[alexjoffroy]

Fix #19

[alexjoffroy]

Hi :)

Tests seems ok, even in 5.4, no ? https://travis-ci.org/eusonlito/laravel-Meta/jobs/383735080

Anyway, when I submitted my PR, I have a fork from commit 51f0b44979d700035eba9c9cd318f33411ba014e, tests were failing with my php 7.x:

PHP Fatal error:  Class 'PHPUnit_Framework_TestCase' not found in .../laravel-Meta/tests/Tests.php on line 4

Fatal error: Class 'PHPUnit_Framework_TestCase' not found in .../laravel-Meta/tests/Tests.php on line 4

Now, when I try from the current master, I don't have this one anymore :) So, I guess I can remove the commit.

Concerning "Class name resolution via Meta::class", is Eusonlito\LaravelMeta\Meta will be OK instead for 5.4 ?

Just as a sidenote, since 5.4 (and 5.5) are not supported anymore, is it still relevant to have support for them on this package ?

[eusonlito]

Done, Thanks!