rustfmt: Change fn_args_layout to fn_params_layout

Running `cargo +nightly fmt` emits a bunch of warnings of form:

 Warning: the `fn_args_layout` option is deprecated. Use
 `fn_params_layout`. instead

As suggested change the `fn_args_layout` option to `fn_params_layout`.

Author: tcharding

rustfmt.toml

@@ -44,7 +44,7 @@ enum_discrim_align_threshold = 0
 match_arm_blocks = true
 match_arm_leading_pipes = "Never"
 force_multiline_blocks = false
-fn_args_layout = "Tall"
+fn_params_layout = "Tall"
 brace_style = "SameLineWhere"
 control_brace_style = "AlwaysSameLine"
 trailing_semicolon = true