Improve assert.throws() error in TAP reporter

[Krinkle]

Test case

QUnit.module( "Throws match", function() {
	QUnit.test( "bad", function( assert ) {
		assert.throws( function() {
			throw new Error( "Match me with a pattern" );
		}, /incorrect pattern/, "match error" );
	} );
} );

What actually happened?

TAP version 13
not ok 1 global failure
  ---
  message: "match error"
  severity: failed
  actual: {}
  expected: {}