adding and removing items from multi-line arrays does not preserve "end-of-array" style

[decathorpe]

It looks like adding or removing items from multi-line arrays does not respect the existing formatting of the "end of the array", i.e. the placement of trailing commas (if any) and closing "]" is not preserved.

1. Appending an element to an existing multi-line array with a trailing comma after the last item results in an array without a trailing comma after the last item:

import tomlkit

test = """\
hello = [
    "one",
    "two",
    "three",
]
"""

expected = """\
hello = [
    "one",
    "two",
    "three",
    "four",
]
"""

actual = """\
hello = [
    "one",
    "two",
    "three",
    "four"
]
"""

data = tomlkit.parse(test)
data["hello"].append("four")

tomlkit.dumps(data) == expected  # False
tomlkit.dumps(data) == actual  # True

2. Removing any element (i.e. this is not specific to removing the last element) from a multi-line array moves the closing "]" to the end of the previous line, even if it was on its own line before:

import tomlkit

test = """\
hello = [
    "one",
    "two",
    "three",
]
"""

expected = """\
hello = [
    "one",
    "two",
]
"""

actual = """\
hello = [
    "one",
    "two"]
"""

data = tomlkit.parse(test)
data["hello"].remove("three")

tomlkit.dumps(data) == expected  # False
tomlkit.dumps(data) == actual  # True

Not only is the placement of the closing "]" not preserved, but it appears to be "blindly" moved to the end of the previous line.
This can actually produce invalid TOML if the previous line contains a comment (already filed as a separate issue: #213 ).

---

Tested with tomlkit 0.11.1.