Label rustfmt toolstate issues with A-rustfmt

This makes it easier to filter toolstate issues by the tool involved.

Author: Aaron1011

src/tools/publish_toolstate.py

@@ -42,7 +42,7 @@
 LABELS = {
     'miri': ['A-miri', 'C-bug'],
     'rls': ['A-rls', 'C-bug'],
-    'rustfmt': ['C-bug'],
+    'rustfmt': ['A-rustfmt', 'C-bug'],
     'book': ['C-bug'],
     'nomicon': ['C-bug'],
     'reference': ['C-bug'],