Fix octave on gray chord

The only person I know who is using the app and on >= gray says it's
fine to make this without trying to keep an option for the old version,
so I'm going to just push this through unless anyone explicitly objects.

_data/chords.yml

@@ -37,7 +37,7 @@
 - name: "gray"
   display: "Gray"
   chord: "A"
-  notes: ["A4", "C#4", "E4"]
+  notes: ["A3", "C#4", "E4"]
 - name: "tan"
   display: "Tan"
   chord: "D"