return error on throw method to chain on error properties

[vbardales]

Allow to create that type of assertions:

expect(fn).to.throw(BadArgumentError).that.have.property('code', 500);

by chaining on the error instance, not on the function that throw an error

[coveralls]

Coverage remained the same when pulling c32ae3e on vbardales:master into 0e560c6 on chaijs:master.

[coveralls]

Coverage remained the same when pulling 2bb0ff2 on vbardales:master into 0e560c6 on chaijs:master.

[vbardales]

up ?

[vesln]

Makes sense to me. @logicalparadox?

[logicalparadox]

👍