Allow sequences in parameter specifications with urlencode

This fixes problems when specifying multiple search criteria. 
Currently, trying to query multiple search criteria fails due to the urlencode not supporting sequences, e.g. this example fails:
```
b = Brightcove('lWCaZyhokufjqe7H4TLpXwHSTnNXtqHxyMvoNOsmYA_GRaZ4zcwysw..')
b.search_videos(all=['tv_show:Offspring','video_type_long_form:Full Episode'])
```
This one-line change fixes this problem by telling urlencode to separate sequences correctly.