geo json merge issue (union)

[Rakesh-webdeveloper]

I'm working on a project, where I need to merge (union) the 2 different cities. But in you lib giving an issue,
Error: Cannot use object of type Polygon as array in
www.xyz.com/martinez-rueda-php/src/Algorithm.php on line 130
This issue is solved. Plz, consider the pull request.

[toanqng]

golang implement: https://github.com/toanqng/martinez-rueda

[miguelfrmn]

@Rakesh-webdeveloper Solved in #5