docs/UPGRADING.md: Minor formatting fixes

Signed-off-by: Gergely Nagy <algernon@keyboard.io>

docs/UPGRADING.md

@@ -566,11 +566,11 @@ The following headers and names have changed:
 
 ### Removed on 2020-01-06
 
-### EEPROMKeymap mode
+#### EEPROMKeymap mode
 
 The [EEPROM-Keymap](doc/plugin/EEPROM-Keymap.md) plugin had its `setup()` method changed, the formerly optional `method` argument is now obsolete and unused. It can be safely removed.
 
-## keymaps array and KEYMAPS and KEYMAPS_STACKED macros
+##### keymaps array and KEYMAPS and KEYMAPS_STACKED macros
 
 The `keymaps` array has been replaced with a `keymaps_linear` array. This new array treats each layer as a simple one dimensional array of keys, rather than a two dimensional array of arrays of rows. At the same time, the `KEYMAPS` and `KEYMAPS_STACKED` macros that were previously defined in each hardware implmentation class have been replaced with `PER_KEY_DATA` and `PER_KEY_DATA_STACKED` macros in each hardware class. This change should be invisible to users, but will require changes by any plugin that accessed the 'keymaps' variable directly.
 
@@ -578,13 +578,13 @@ Code like `key.raw = pgm_read_word(&(keymaps[layer][row][col])); return key;` sh
 
 ### Removed on 2019-01-18
 
-### Removal of Layer.defaultLayer
+#### Removal of Layer.defaultLayer
 
 The `Layer.defaultLayer()` method has been deprecated, because it wasn't widely used, nor tested well, and needlessly complicated the layering logic. If one wants to set a default layer, which the keyboard switches to when booting up, `EEPROMSettings.default_layer()` may be of use.
 
 `Layer.defaultLayer` has since been removed.
 
-### More clarity in Layer method names
+#### More clarity in Layer method names
 
 A number of methods on the `Layer` object have been renamed, to make their intent clearer: