Allow overriding template with extend

[timwis]

This allows you to override the default template using

var myTemplate = '<select>...</select>'
var MySelect = SelectView.extend({ template: myTemplate })`

(which doesn't currently work).

This works the same way ampersand-input-view does it

[timwis]

FYI, the travis error message regards no saucelabs credentials being provided, so I'm assuming it's not to do with the code change

[wraithgar]

This is one of those tweaks that leaves one wondering "why didn't we do this in the first place?"

Thanks for your PR. Yes the test failure is due to a security constraint in travis.

Wondering if a readme update is in order for this or not.

+1 on the code pending readme discussion.

[cdaringe]

+1

[cdaringe]

i will update the README and publish

[wraithgar]

Thank you @timwis!

[cdaringe]

published as 6.2.0! thx