Changing tourism=picnic_site icon colour to green

[kocio-pl]

Resolves #2915.

Example place with both tourism=picnic_site and leisure=picnic_table:

Before

After

[kocio-pl]

Any reviews or comments?

[turnsole80]

This is a good change.

[polarbearing]

Isn't tourism brown and leisure green? So, should the colours assigned vice versa?

[kocio-pl]

Thanks, that's a good point! I think both keys are misleading in this case: picnic table is like other general amenities, especially bench, since it's rather about a rest than physical activity, while picnic site is also closer to recreation area (I would say it's really just a subtype of such area).