refactor bubble

src/Aquarium.cpp

@@ -91,7 +91,7 @@ void Aquarium::redraw() {
     auto &bubble = *it;
     bubble->draw();
     bubble->update();
-    if (bubble->getY() < 9)
+    if (bubble->isOutOfWater())
       it = bubbles.erase(it);
     else
       ++it;
@@ -137,7 +137,7 @@ void Aquarium::redraw() {
   applyBackBuffer();
 }
 
-void Aquarium::addBubble(float x, float y) {
+void Aquarium::addBubble(size_t x, size_t y) {
   bubbles.emplace_back(std::make_unique<Bubble>(x, y));
 }