Set rustfmt comment and line width to 100

It was a bit weird that the `comment_width` was configured to be
_longer_ than the `max_width` which sets the maximum width of each
line.

I choose to explictly set `max_width` to its default value of 100 for
clarity.

The reason why we don't see any other changes to the diff should be
obvious: setting `comment_width` to more than `max_width` was useless!

Inspired by:
rust-lang/rustfmt#3349 (comment).

dprint.json

@@ -5,7 +5,8 @@
   "rustfmt": {
     "imports_granularity": "item",
     "wrap_comments": true,
-    "comment_width": 120
+    "comment_width": 100,
+    "max_width": 100
   },
   "sql": {
     "uppercase": true