Editorial: Minor fix in evaluation of 'YieldExpression' and Arguments Exotic Object

[h2oche]

• In 15.5.5 Evaluation, value is defined twice in step 3 and step 7.c.viii.1. I think using Set ~ to ~ notation is more proper in step 7.c.viii.1.
• In [[DefineOwnProperty]] and [[GetOwnProperty]] of 10.4.4 Arguments Exotic Object, abstract operation Get should not return abrupt completion since existence of property P in map is checked by HasOwnProperty.