Needs to retry on failure to retrieve tiles

[teo1978]

When a network error occurs while trying to retrieve the tiles from the provider, mapstatic should retry up to a configurable maximum number of times and waiting a configurable delay between retries.
If, after that, it still fails, then it should print a meaningful error message.

Instead, it only tries once, and in case of failure it throws an exception whose cause is very hard to figure out. This way, using mapstatic for example on a server to programmatically generate static maps is almost impossible, because it is completely unreliable.

[amansingla32]

You can catch the failure and retry yourself as well. I know including it in the gem itself would have been great but this is how we are using it