Replace the array_merge with spread array operator

[peter279k]

Changed log

• According to the reference, it's great to use the spread array operator to replace the array_merge function.
• There're two reasons about using the spread array operator:
  • Spread operator should have a better performance than array_merge and compile time optimization can be performant for constant arrays.
  • array_merge only supports array, while the spread operator also supports objects implementing Traversable.

[michaelpetri]

Thanks for the addition