Use JSONAssert to assert on json strings

Rewrite all tests assertions on json strings using JSONAssert. Fix #162.
Previous order was wrong I think, because the 2 Person instances are created this way:
```
Person("Mr Bean", "mrbean@outlook.com", 64)
```
and not
```
Person("Mr Bean", 64, "mrbean@outlook.com")
```
And I preferred swapping on one line instead of two