Changing game state through the dedicated methods (eg. Game#running!)

Thoses methods are nice, not using them would be a shame.

Do note, however, that they are _not_ used in the specs for the `Game` model.
I felt like staying low-level and keep the specs code below the abstraction of
those methods made more sense.

Author: r3trofitted

app/dispatches/bombs/drop.rb

@@ -82,7 +82,7 @@ def successful_payloads
 
     def finish_game
       player.update(won: true)
-      game.update(state: 'finished')
+      game.finished!
     end
   end
 end

app/dispatches/players/enlist.rb

@@ -13,7 +13,7 @@ def initialize(game:, player:)
 
     def assign_game_to_player!
       @player = Player.create!(nickname: nickname, game: game, life: Player::LIFE)
-      game.update(state: 'running')
+      game.running!
 
       return successful_payload
     end

spec/requests/opponent_spec.rb

@@ -37,7 +37,7 @@
 
     context 'when game is full' do
       before :each do
-        game.update(state: 'running')
+        game.running!
         game.players.create!
         post "/games/starship-battle/opponent"
       end
@@ -54,7 +54,7 @@
 
     context 'when game is already finished' do
       before :each do
-        game.update(state: 'finished')
+        game.finished!
         post "/games/starship-battle/opponent"
       end