tweak the description

"in addition to" sounds better than "additionally to"

Author: nikomatsakis

src/librustc/session/config.rs

@@ -1058,7 +1058,7 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
     dump_mir_dir: Option<String> = (None, parse_opt_string, [UNTRACKED],
           "the directory the MIR is dumped into"),
     dump_mir_graphviz: bool = (false, parse_bool, [UNTRACKED],
-          "additionally to `.mir` files, create graphviz `.dot` files"),
+          "in addition to `.mir` files, create graphviz `.dot` files"),
     dump_mir_exclude_pass_number: bool = (false, parse_bool, [UNTRACKED],
           "if set, exclude the pass number when dumping MIR (used in tests)"),
     mir_emit_validate: usize = (0, parse_uint, [TRACKED],