Remove short array syntax and make it compatible for 5.3

[harikt]

Have removed the type callable from

-    public function __construct(callable $factory)
+    public function __construct($factory)
     {
+        if (! is_callable($factory)) {
+            throw new \Exception("Should be callable");
+        }
         $this->factory = $factory;
     } 

https://github.com/harikt/Aura.Input/commit/8f374c1acb243932b089fafef811ddee710fd572

The exception can be moved to its own place.

https://travis-ci.org/harikt/Aura.Input/jobs/8448918

Let me know your comments

[harikt]

seems we want to change the composer.json also . And I guess you need to move the exception to a seprate place. So please don't merge this.

@pmjones let me know your comments on the same.

[pmjones]

Are we still thinking that we want to port some stuff backwards to 5.3?

[pmjones]

The consensus so far is that we are not porting back to 5.3.