[1.x] Make aggregateTotal return a float when a single type is requested

[jessarcher]

This PR improves the return value of the aggregateTotal method when only a single type is requested.

$total = Pulse::aggregateTotal('cache_hit', 'count');

// Before

Illuminate\Support\Collection {
  #items: array:1 [
    "cache_hit" => "12.00"
  ]
}

// After

12.0

The current return type is maintained when passing the first parameter as an array of types.