Update assert.js

- is.not.throwing() threw an exception in negate() because the success case of throwing() didn't return a "message" property in the return object. But the function negate() accesses this property regardless of the state of "success". I fixed this by ading a message property in throwing() in the success case.

- added functionality that is.ofType() recognizes arrays not only as objects but as arrays also:
assert.that([], is.ofType("object"));
assert.that([], is.ofType("array"));

- added double quotation marks in messages for all outputs of "actual" and "expected" for better readability of the mocha console output, especially when the text in those variables is longer than a few words.