Always use trailing newlines in multi line arrays

[vektah]

#1461 switched to using multi line toml arrays in the lock file, while this improved readability it also introduced some additional diff churn.

Before:

- packages = [".","a"]
+ packages = [".","a","b"]

After:

packages = [
    "."
-   "a"
+   "a",
+   "b"
]

This is bad because it increases the chance of merge conflicts in the lock and decreases readability. It was also one of the reasons toml was chosen over a more mainstream format like json.

Proposal: Always add trailing commas, just like in go. This probably requires an upstream change to the toml library.

[vektah]

Sorry, double post of #1595